How to implement a simple EDS?

Question

Document flow

The task is simple:
1 send .doc or .pdf
2 by email or write to the cloud
3 with some digital signature
4 free
5 so that at the other end this signature can be certified in some way by unqualified employees (who simply accept forms and enter indicators into a computer).
This is a commercial (i.e. not a state / budgetary organization). So just about any method can work, as long as it's convenient and free.
As a result, it is necessary to transfer this method to other reporters, so that the signature method is also desirable for the teanoks to be understandable.
And if it can be implemented with something ready for PHP, i.e. an online service would be just lovely. I would drink such a free service for the city.

Answer 1

In a simple way, this is done, for example, through pgp and a plugin in thunderbird.