With PDFBlackbox you can complete your PDF processing applications with outstanding security features, such as password-based and certificate-based encryption, certificate-based signing and compression of your PDF documents.
General PDF features, supported by PDFBlackbox are:
support for PDF format versions 1.3 to 1.6
PDF standard password-based data encryption using MD5 + RC4/40 or
RC4/128 or AES/128 algorithms
PDF certificate-based public key data encryption using RSA algorithm and PKCS#7 format
certificate-based data signing using SHA1 with RSA algorithms and
PKCS#1 or PKCS#7 format
data timestamping using TSP (Timstamping Protocol)
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.