PDF In-Depth

PDF Collaboration: WebDAV In Action

July 03, 2001


Editor's Note: Planet PDF is hosting a free WebDAV demo, providing a chance for Acrobat 5-equipped users to test the program's online reviewing and comments-sharing capabilities. This article is also available in PDF.

"Adobe Acrobat 5 will allow document creators, managers and producers to view, annotate and approve PDF files online. We tested these features and examined their strengths -- and weaknesses -- as collaborative publishing tools."

Traditional, linear approval processes are generally at odds with shrinking deadlines, multi-departmental review processes and the needs of cross-media production. Electronic files, including Portable Document Format (PDF), have often merely exacerbated the problem. Although they can be transferred more Rapidly than their paper counterparts, they are still handled in the conventional way: One person looks at the document and the previous comments, makes additional comments, and sends it on to the next person. (In fact, all too many reviewers will print out a PDF before marking it up, negating much of its value.)

Collaboration Simplified

Collaboration Simplified

To begin the process, PDF files are first uploaded to a Web server. With the full version of Acrobat 5, users may add comments to the online PDF, and even attach files -- including the original source file, if desired. After everyone has made comments, a facilitator must reconcile the comments, using a variety of tools in Acrobat, and use them as a guide for making the required changes in the source file.

To remedy this problem, numerous vendors have developed network-savvy methods for viewing, annotating and approving server-resident electronic files. Most of these involve the creation of a rasterized version of the page that is viewed on either a standard browser or a customized client application. Authorized users then add comments (usually as electronic "sticky notes") and other marks.

However, these systems? advantages -- centralized data control and relatively simple browser access -- are for many users, offset by a combination of negative factors. Most collaboration systems are proprietary in nature, raising doubts about connectivity with other systems, high cost or the life expectancy of the developer or ASP providing the service. In addition, few (if any) of these systems fully utilize PDF or its underlying data structure.

To be sure, earlier versions of Acrobat provided on-screen annotations. Users could even export such comments as small data files, using Adobe's Form Data Format (FDF), which could then be imported into another copy of the same PDF file. However, until version 5, many users considered this manual process too cumbersome.

Acrobat 5 Online

PDF files have long been viewable from a Web browser, using a free plug-in for Communicator or Internet Explorer. Previously, however, the comments or annotations could only be viewed, not created. One of the significant new features of Acrobat 5, released in April, was the ability to add comments and digital signatures online. Although Adobe's tools are rudimentary, they form the basis of a collaborative workflow that is based, not on a proprietary raster file, but on PDF, which is widely recognized as an open, flexible and data-intensive format.

Safety First: Adobe's Security Mechanisms

While the recipient can quickly judge the authenticity of paper documents by standard identifying marks -- signature, letterhead, corporate seal -- it has been impossible to do the same for electronic files. Acrobat offers a number of security mechanisms to help with this. First, a file can be protected against possible modification with 40-bit or 128-bit RC4 encryption. The user can choose whether the file is protected against being viewed, changed, printed or copied, as well as whether selected data can be copied and whether annotations can be edited or removed.

Next, the file can be provided with a digital signature -- the Acrobat Self-Sign Certificate. The recipient can check for the correct "user certificate." This requires the sender of the file to send a copy of the certificate separately and also to import the same certificate into the Acrobat application. Then, upon receiving a document with a digital signature, the recipient's copy of Acrobat can compare the certificates and identify the sender. Since the certificate is doubly password-encrypted, the sender need have no concern about forwarding it to the recipient. The sender also can have confidence that the document has not been altered; this would immediately be flagged.

The Basic Workflow

Acrobat 5's online workflow means that a PDF can be uploaded to a Web server, viewed in a browser by any prospective collaborator, and annotated online. Multiple users may view online PDFs, but must upload and download comments as a separate step. After everyone has reviewed the file, a facilitator must act upon the comments -- usually by editing a copy of the source file. Optionally, he or she may also download the PDF, with all its comments, for reference.

To participate in this process, users must have the full version of Acrobat 5, not simply Reader or Adobe's new forms review product, Approval. Online digital signatures are possible, but the process is separate from that of online comments.

A separate server is required to hold the FDF files created by this commenting process. Adobe provides two methods for doing this: designating a shared folder on a network server, or specifying the URL of a WebDAV server. (Both procedures are described below.) Although it is easy to set up, the shared folder method is problematic because all users must have access to the same server, making it feasible only in an Intranet environment. WebDAV (short for Web Document Authoring and Versioning) is much harder to configure, but it allows anyone with an Internet connection to participate.

There is a further potential to online collaboration in Acrobat. FDF files -- which can contain both comments and forms-based data -- are a potential source of valuable information for business or workflow-management systems. Using Adobe's FDF Software Developer Kit (SDK), available at partners.adobe.com, developers can extract meaningful metadata from FDF files and can submit it in a Web environment using an XML flag. However, the SDK is somewhat vague on exactly how this is done.

Although standard forms-data submission is fairly common, it is too soon for developers to have employed similar tasks with online comment data. Undoubtedly, this will start to happen with a variety of business and workflow systems, especially when the Job Definition Format (JDF) becomes more widespread.

Acrobat's Toolbox

Commenting Toolbar Before we go into the online aspects of Acrobat 5, it is important to understand the tools themselves. In the full version of Acrobat, a variety of text and graphic markings can be applied to a PDF file, and text passages can be highlighted. The tools for enriching a PDF file with additional information, combined with easy identification of the author of each annotation, are the basis for virtual collaboration on digital documents. Adobe classifies Acrobat's annotation tools into three groups, as shown at right.

The first five tools are for commentary. They include a Notes tool (a digital version of the "sticky note"), a Free Text tool for placement of arbitrary lines of text, and a Stamp tool for placing user-defined images, such as "Draft" or "Confidential." Even audio comments and source files can be appended to the PDF, using the Sound and File Attachment tools. We think audio comments are of dubious benefit, since they add considerably to file size. (Of course, they might have enormous value to blind users.) However, the ability to attach files is certainly valuable, although the attachments can be read only if the recipient has the authoring application. File attachments also increase overall file size and, as actually happened recently, can be used to spread viruses.

The second group, graphic marking tools, includes a free-form Pencil tool, and self-explanatory Square, Circle and Line tools. The final group, text annotation, includes a Highlight marker tool, a Strikeout tool and an Underline tool. (The "Commenting" toolbar, shown here, also includes a spell-check tool for comments, and the Digital Signature tool. The latter does not actually create FDF data, as we will discuss below.)

With the exception of the Sound and File Attachment tools, every tool creates data that can be saved as a text file. In addition, the selected text is copied into the annotation window, giving the user an easy opportunity to suggest an improvement. This text can be spell-checked, and the text window can be moved, resized and (in Acrobat 5) made semi-transparent.

Users may specify a unique color for their annotation boxes, and annotations may be sorted (by author, date, page or type) in the Comments portion of the Navigation pane. Pages can be printed with or without comments, and Acrobat includes a variety of tools to summarize, filter (suppress) and find comments.

Role of FDF

Importing and exporting annotations (FDF files) is handled via the Comments pane, or from the File menu. Prior to Acrobat 5, passing FDF files from users making comments to users following their instructions was the only practical way to conduct a virtual editing cycle. (The alternative, annotating a PDF and sending the entire file to the next user, was impractical because of large file sizes and serious version-control issues. Swapping FDF files was not trouble-free, however. Although the files are small and can be e-mailed easily, the same version-control problems exist.)

Say What?

Commenting Toolbar

When a shared folder is used to manage online comments, the designated folder receives FDF files within folders named for cross-platform functionality. A single user's FDF file will always have the same generic name.

Adobe developed FDF as a "transport format" for flexible transfer of information. For example, it is used for transferring the contents of tables or fields. The FDF format is based on the syntax of PDF. Its descriptions of objects and data are similar to those used by PDF itself, and they offer many options for display. Using this transport format, it is possible to forward and exchange data collected from forms, notes and annotations, and even optical markings.

On a small scale, this worked out very well if one had the PDF file as well as the associated FDF file on a local hard disk. However, if the user wanted to leave the PDF file on the server without transferring it from one user to the next, matters became complicated and generally impractical.

In version 5.0, Adobe has carried the comments concept a step further. Both PDF files and annotations can be accessed via the Internet or a local Intranet, using current industry standards such as WebDAV and Microsoft's Web Discussions. Data exchange via SQL and folder-based FDFs within a local network can also facilitate the process.

Our Test

We undertook a brief "proof of concept" test of several techniques for working with PDF files online. While these were not comprehensive tests, they did indicate some of the obstacles for the do-it-yourself approach, and they revealed a number of issues that Adobe -- or its integration partners -- must address. Our test scenario -- revising an article for a publication -- easily could be applied to designing a piece of print collateral or even making remote annotations to a legal document.

Network Folder Setup

Adobe's technique for using a shared folder for online comments is extremely straightforward. Each Acrobat 5 user must simply specify a server path in the "Preferences > Online Comments" dialog. In our test, we specified a folder within a Macintosh-accessible volume ("SHARED:Annotations:") on a server running Windows NT 4 ("D:\SHARED\Annotations\").

That's Easy for You to Say!

WebDAV server setup

Once configured, the Web server and the WebDAV server act in tandem. One manages PDF files uploaded via FTP, while the other manages corresponding FDF files. Except for PDF uploading, all file transfer and viewing is handled via HTTP.

When we opened a PDF file on a separate Web server, Acrobat 5 automatically created FDF files on the server volume.

Acrobat encodes FDF file- and folder-names in a manner that will be usable across different platforms. Although duplicate IDs are theoretically possible, in practice they are exceedingly unlikely. (The math exactly parallels the so-called "birthday problem." The collision probability only reaches the 50 percent level if you have at least 264 files.)

The obvious drawback to the shared folder method is that all users must have the same server access. In most cases, this means access to the same LAN or a robust corporate WAN. Remote users, even those with a reliable Internet connection, are excluded.

Another difficulty is the anonymous nature of the FDF files on the server. Although Acrobat can connect an online PDF with its respective FDF file(s), there is no efficient, external method for doing so. Identifying a specific FDF file can be done only by opening it in a text application, and then searching the File ("/F") string. There is also no easy way to delete unused FDF files, which will eventually clutter up the server. A better selection of FDF parsing and management tools is clearly called for. (The SDK mentioned earlier does not deal with FDF files stored on a shared folder or a WebDAV server.)

WebDAV: All That Glitters is not Gold

  • A technical description of the installation and setup we used for our WebDAV testing, including the problems we experienced.)

Installing and configuring WebDAV was a difficult and frustrating task. The technology is still in its infancy. Numerous suppliers are converting their servers to this new standard, but not without problems.

In spite of these problems, we finally managed to configure a WebDAV server, physically located in the U.S., that could manage FDF files and relate them to PDF files on a separate Web server located in Germany.

It's important to note that, in this design, WebDAV is receiving FDF data files containing user annotations, not the actual content of the PDF. Other Adobe WebDAV plans, centering on its content-creation applications (InDesign, Photoshop, Illustrator, GoLive, LiveMotion, etc.), will use WebDAV in an entirely different manner. WebDAV-enabled products such as InScope and Adobe Studio will allow users to "check out" and "check in" various content files, as well as track file versions and a variety of job-related metadata. Acrobat is somewhat unique, in that the job content is static, while the comment metadata is dynamic.

An important advantage of WebDAV is that the implementation of this technology requires few system resources. This improves the overall behavior and performance of the Web server, which explains why many Web administrators are so fond of WebDAV. The normal user of a Web server won't get a chance to experience the benefits of a comprehensive WebDAV-HTML environment until sometime around the end of 2001. But when that time comes, it will be Acrobat users who are best equipped to benefit.

Test Results

Opening and working with online PDFs was strikingly similar to doing so locally. Pages opened relatively quickly (using an ISDN connection), and file navigation was identical to using Acrobat alone. Naturally, some features, such as Link creation, were not available. Pages could be rotated, but the rotated state could not be saved. (Saving an online PDF copies the file to the local drive.) As with Acrobat itself, users can zoom up to 1,600 percent, revealing vector-quality detail. Rendering of vector objects is vastly superior to other online systems that rely on bitmap rendering.


Successive User Comments

Successive users can add a wide variety of comments to online PDF files via Acrobat 5. Comments can be sorted by various criteria. The resulting file may also be downloaded along with its comments, which can be summarized for final review. [Click image to view full version.]

Testing the various Acrobat comments was also satisfactory. Multiple users added a variety of annotations, which were successfully preserved using both the shared folder and WebDAV methods.

The annotations are time-stamped and identified with the author's name. However, outside of Acrobat itself, there are no tools (yet) that can extract meaningful data from the stored FDF files and convey it, via XML or otherwise, to an external management or workflow system. During our testing, we learned of several companies in the process of integrating Acrobat and WebDAV, but none were prepared to share their findings. (In a future article, we will detail some case studies, as well as discuss some upcoming products that relate to online PDF collaboration.)


In general, we were pleased with the results of our tests, and we can certainly see the potential for online comments -- not only in graphic arts and publishing, but wherever documents need to be created, reviewed and revised by a distributed workgroup. Dealing with a single PDF file and combining it with multiple comments (in a straightforward Web environment) is attractive, once the initial configuration problems are overcome. The decreased volume of transmitted data and the potential for centralized management makes the process well worth looking at. We encountered several problems with this workflow.

One was the lack of practical administrative tools, although we believe this will be remedied shortly by third-party developers. Another issue was our disappointment -- from the graphic arts perspective -- over the file-transfer requirements of using digital signatures online. (See the "Signatures and Forms" page.) Acrobat's commenting tools, both online and in the stand-alone product, were sometimes awkward. (As editors, we found that the electronic tools often required more steps than the manual markup process, or contained annoying limitations such as the inability to highlight a whole paragraph in a multi-column layout.)

One significant barrier to this workflow is price. The full $249 version of Acrobat 5 is required for users to view online comments, even if the user does not need to make comments. Neither the free Reader nor the recently introduced Approval product ($39) can view WebDAV-hosted online comments. For users who need only to view and approve comments, we would strongly suggest a read-only WebDAV feature be added to the next version of Approval.

Acrobat's online capabilities have increased the potential for collaborative workflow, using a common file format and (at least for comments) the obvious strengths and popularity of WebDAV. As tantalizing as this potential is, however, we feel the process is unfinished, and that practical solutions are still to come.

About the Authors

Bernd Zipper (zipper@zipcon.de) is a business and technology consultant specializing in PDF, new media and cross-media publishing projects. He is president of ZIPCON NewMedia and Prepress Consultinggesellschaft mbH (www.zipcon.de) in Essen, Germany.

John Parsons is Senior West Coast Editor for The Seybold Report.

Seybold ReportsRepublished with permission from The Seybold Report.

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