http://tinyurl.com/hqfbncd
First link - how to sign PDF documents
Second link - Learn how to Digitally Sign Files, Documents, Emails
3) How to Digitally Sign a document with Adobe Reader
4) PDF Signer Free – Digital Signature Software
5) Get or create your own digital signature - Office Support
6) How to Sign Documents and Fax Electronically [E-signatures]
7) + 8 ) Wikipedia
9) The 24 Best Apps to Digitally Sign, Scan and Fax Documents
10) Howto: Add a Digital Signature to a PDF File
Results: 0 relevant links on the first page. On other pages some links are suggesting buying some stuff from Microsoft and that is not free!
After more googling and changing search phrase I have found
kSign but it needs some PFX file with certificate. And I did not found where I can get one for free.