I've always used Encrypt with password to not allow changes and then after this signed with an invisible digital signature. On exactly the same permission files often the Sign with Invisible signature option is blanked out/unavailable. Why would it be available only sometimes? Is this a bug in Acrobat Pro DC? Is there a way to enable it to sign my encrypted PDFs? I find if I remove the Password encryption, re-apply it then signing is available (sometimes). Very frustrating.
Have DC Pro 15.009.20077.29851
Thanks for helping!
Maybe this will help someone, but after checking a bit more, it seems if you apply the password encryption, the trick is not to save the file but sign immediately, this will prompt to save. If you save first the file is tagged as SECURE and then you cant sign i anymore. This is a bug I guess.
Another annoying one is when applying a background the settings in a saved profile defaults to inches regardless as what you've saved the background profile.