This has been a fairly common issue with the old style SHX fonts from AutoCAD and the text is appearing something similar to the following:
There are a number of contributing factors in this one but I’d say the main one is that Revit only officially supports the use of TrueType fonts and the recognition of the SHX fonts is somewhat limited. The text display of these imported fonts is based on the defining SHX font lines and these are quite thin to begin with and not particularly easy to control.
Added to this is the fact that when these are output to a PDF they are normally printed as thin linework and not recognised or processed as fonts. Due to the accuracy limitations of the PDF format it becomes highly likely that it will fail to reproduce the thin defining lines of the font.
So, the upshot of this is that the Waterman standard font within Revit is Arial.