PDFTron's PDF Secure is a stand-alone application that provides users with
an affordable and reliable means of adding, removing, or changing security
settings on existing PDF documents or whole directories of documents. PDF
Secure is offered as an easy-to-use GUI (Graphical User Interface)
application and as a command-line application.
Using PDF Secure, standard PDF bit encryption (40 and 128 bit) can be
applied to any existing PDF document or to whole directories of documents.
Security settings (e.g. changing passwords and security permissions) can
easily be modified and all standard options and permissions can be
specified directly through an intuitive interface.
Key Functions of PDF Secure:
Apply standard PDF 40 and 128 bit encryption to any existing PDF
document or whole directories of documents
Modify security settings (e.g. change passwords and security
Supports PDF 1.5 and Acrobat 6 documents
All standard options and permissions can be specified:
Set or modify user and owner
'Print' and 'high resolution print' permission
Modify document's contents
Copy or extract text and graphics
Add or modify text annotations; fill in interactive form fields
Set, create or modify interactive form fields
Fill in existing interactive form fields
Extract text and graphics (in support of accessibility to disabled
users or for other purposes)
Assemble the document (insert, rotate, or delete pages and create
bookmarks or thumbnail images)
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.