PSP applies or removes Acrobat standard security features to PDF files. PSP can apply user and master passwords, and set access permissions to prevent printing the document with Acrobat, extracting text, modifying the document, etc. PSP uses 40-bit or 128-bit encryption keys. 128 bit keys have been introduced in Acrobat 5, and are also known as "secure" keys.
With PDFlib PSP you can do the following:
Encrypt a PDF document with a user or master password (or both)
Remove PDF encryption if you know the document's master password
Add or remove permission settings (e.g., printing or text extraction not allowed) if you know the document's master password
Query information about the security status (encrypted with user or master password), encryption scheme (Acrobat standard security, WebBuy, etc.), permission settings, and document info fields
PSP is not a cracker tool – it cannot be used to gain access to protected documents without knowing the (appropriate user or master) password.
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.