The "shxfontmap.txt" is located at:
C: \ Users \
First you should make a backup copy of "shxfontmap.txt" are created, they can then be opened with Notepad.
Note: Please do not use software to edit the file, which could change the formatting of text, such as Word.
At the end of the file is then added to "txt.shx Arial" or "Arial italic8.shx" added.
After the names of the SHX once is "Tab" and then use the new font specified."
Autodesk BIM Blog - Darstellung von SHX Schriften f�r DWG Dateien anpassen - Revit Architecture/MEP/Structure 2013