PDF signing feature backported from 4.4

Cherry picked from:
840f75065918c4584fa9159fdc90242b5374ab37
1fe9ee73a758603ee0e1465931352c41ef8bd999
d8a8ff8177df628636d80c4dc1d8f597f6677dfc
bfa01d8a8248f7e44675de5ed1f85a1d17105022
bbb18f679f5a50e9c709520d6c3260d3d9db5aa9
c4cc31b5b55019aabad4045c8174b45e1b27073a
7e3c931786c3cbe83ee170b8b0746d141b520ce6
070c93af73df9aa4eb333265c81060d123b530b9
6e91763769a562b88882a4c2a94b1367c6ed4866

Change-Id: Ie8ac5e1e067f8e3b15e2f11389bd0517d348f1e3