Every once in a while Revit will swap out the text on our sheets for different characters in PDF prints. This happens across different PC's in our office from time to time. We use Bluebeam PDF for the PDF exports. My latest example happened on a 48-page PDF, where 47 of the 48 pages printed normal and one sheet in the middle has all the text changed to strange characters. See images below:
Printed PDF:
In Revit:
