Isn't PDF perfectly suited for graphic arts? Wasn't the format developed for print and publishing? What can be so terribly wrong with my files then?
Actually, PDF was not developed for use in graphic arts at all. It was developed as a format for the Internet and enterprise world and until the third revision of the language it was generally unusable for graphic arts use. The file format has evolved of course, and the latest versions of PDF (starting with PDF version 1.3) are perfectly suitable for a wide spectrum of graphic arts applications.
That inheritance caused a lot of non-graphic arts features to be built into the PDF file format. It makes PDF so versatile, but also presents a danger for graphic arts workflows. What happens if you include a sound fragment or a movie in a file that is going to be printed? There are plenty of opportunities to create a PDF file that will not print correctly or not print as expected. Let's look at some of them.
Different PDF Versions
The original PDF version was (logically) 1.0. Right now we're up to version 1.5. That poses a problem as not all software and hardware can handle the latest versions of PDF documents. Being able to have transparent objects in a modern PDF file is a cool feature, but not all RIPs out there will know what to do with such a file.
The large majority of graphic arts workflows are based on CMYK and spot (named) colors. PDF files allow for much more than that; they support RGB, LAB and different types of color managed colors (the PDF Color Learning Center will tell you all about it). Sending such colors to a press might result in the press just giving up and print nothing; or in hideously wrong colors being printed without further warning.
PDF files support images in any resolution. Low resolution images might look acceptable on screen, but when printed they will look a lot less impressive.
PDF is very versatile with regards to fonts; from the very beginning the format was designed to alleviate font problems by supporting font embedding. If a font is embedded, the designer doesn't have to send it with the document as often happens with QuarkXPress or Adobe InDesign documents. All information needed to display that font is present in the PDF file itself. Unfortunately, a font does not have to be embedded when the PDF file is created. If it is not embedded, Adobe Acrobat will fake it on screen, but a printer will either not print the file or print it totally wrong (substituting the missing font with Courier for example).
Notice that a number of these problems will not at all be visible when you preview the file with Adobe Acrobat. Only specialized preflight software will pinpoint those problems so that they don't slip through.
These problems don't mean that PDF isn't a viable format for graphic arts use. It does mean that proper care must be taken to create PDF files correctly and that you shouldn't just assume any PDF file is automatically good for print.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.