There is only one file type that uses the .TFM extension:
TeX Font Metric File
Font file created for typesetting fonts in TeX and LaTeX documents; does not contain the font glyphs (characters) themselves, but contains information about a font, such as the height and width of the glyphs; required by TeX typesetting and allows a font in a separate file to be typeset in a TeX document.
TFM files can be generated from TrueType (.TTF) fonts using ttf2tfm. They can also be generated from Adobe Font Metric (.AFM) files using afm2tfm. Both programs are included in many TeX and LaTeX bundles. Other font formats are also used with TFM files, such as METAFONT (.MF) files.
Updated: June 4, 2011