The lm fonts are an exciting addition to the armoury of the (La)TeX user: high quality outlines of fonts that were until recently difficult to obtain, all in a free and relatively compact package. However, the spartan information file that comes with the fonts remarks “It is presumed that a potential user knows what to do with all these files”. This answer aims to fill in the requirements: the job is really not terribly difficult.
Note that teTeX distributions, from version 3.0, already have the lm fonts: all you need do is use them. The fonts may also be installed via the package manager, in a current MiKTeX system. The remainder of this answer, then, is for people who don't use such systems.
The font (and related) files appear on CTAN as a set of
single-entry TDS trees —
fonts, dvips, tex and doc. The doc
subtree really need not be copied (it's really a pair of sample
files), but copy the other three into your existing Local
$TEXMF tree, and
update the filename database.
Now, incorporate the fonts in the set searched by pdfLaTeX,
dvips, dvipdfm/dvipdfmx, your
previewers and Type 1-to-PK conversion programs, by
$TEXMF/dvips/config/updmap and insert an absolute path for the lm.map just after the line that starts extra_modules=“ (and before the closing quotes).updmap --enable Map lm.map
updmap.cfg as described in the MiKTeX online documentation. Then execute the command initexmf –mkmaps, and the job is done.
To use the fonts in a LaTeX document, you should \usepackage{lmodern} this will make the fonts the default
for all three LaTeX font families (“roman”, “sans-serif” and “typewriter”). You also need \usepackage[T1]{fontenc} for text, and \usepackage{textcomp} if you want to use any of the TS1-encoding symbols. There is no support for using fonts according to the OT1 encoding.
Source: Using the Latin Modern fonts