Forgery can refer to creating a document and assigning that document to
some other source. For example, in the 18th Century there was the famous
forgery of Ossian, supposedly an ancient celtic writer discovered by the
man who in fact had written it. Also shakespeare plays have been forged:
The forger would pretend to have discovered a elizabethan ms. containing
a hitherto unknown play by Shakespeare. And so for th and so on. The
Protocols claimed to be documents handed down in Jewish tradition. So
they were forgeries. The word has many other senses than that in the
sense of forging a check.

If someone posted a message allegedly from me, and  was able to put my
return address on it, that would be a forgery.

Carrol