To map fonts, edit shxfontmap.txt using a text editor. This file resides in the following location: %APPDATA%AutodeskRevit
For each TrueType font to map, add a line with the following format:
filename.shxFontname
where:
  • filename.shx is the name of the AutoCAD SHX font to map from
  • is the TAB key on the keyboard
  • Fontname is the font to be mapped to
Save and close the file.

You do not need to restart Revit for the font mapping to take effect.

Via
https://twitter.com/RTVTools/status/458699381047173120

Read more / copied from: http://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2014/ENU/Revit/files/GUID-87119589-ADE4-41AD-A796-3EB3C1DDDA82-htm.html