You might wish to convert a LYX Document to a LATEX file. For example, a co-worker or co-author who doesn't have LYX might want to read it. This is very easy to do with LYX. Select File Export LaTEX. This will create a file whatever.tex from the whatever.lyx file you are editing. LYX always creates temporary LATEX files when viewing or printing files, so it is very good at generating LATEX.