Digital Signature and user rights for drawings

I am looking at getting a digital signature for signing drawings or
emails and am wondering if anyone else uses a digital signature. If not
what are you are your companies procedures for file protection of
drawings? I am not very familiar with digital signatures so I am not
sure if the questions is even viable.

My concern is when sending a part with tolerance call outs for a
another company to make parts for us. The parts need to fit our parts
we are manufacturing. What if their is an issue with fit and fuction
down the road and we need to reference the drawings, couldn't the
company in question alter their drawing and say it was the original.
Then it would become a question of who has the unaltered drawing,
basically we would probably have to bear the loss and move on.

Are you guys using other means of file protection like sending the
drawings with read only rules? That way if the customer wants to change
something they would have to change the file name right? Anyway share
your info with me on these subjects please.