iSafePDF is a free open source utility to encrypt, digitally sign and timestamp your PDF documents, after using it, the encrypted document will still be viewable with any PDF reader (if you know the password), the program is very easy to use, divided into tabs, each one of the tab can carry out a function, like encryption and digitally signing the document, there are additional security options to stop document printing and modification.
iSafePDF document digital signature
You can create a time stamped signature using a Time Stamping Authority (TSA), making your digital signature valid even if the certificate key expires, in the Document tab you can change the PDF MetaData information, like author, title, subject and keywords (to find the PDF easily).
This free software to encrypt and digitally sign PDF documents is portable, no installation is needed to use it, the only downside it is that documents can only be encrypted/digitally signed one at a time, it has no batch processing.
