# eqn > Equation preprocessor for the groff (GNU Troff) document formatting system. > See also `troff` and `groff`. > More information: . - Process input with equations, saving the output for future typesetting with groff to PostScript: `eqn {{path/to/input.eqn}} > {{path/to/output.roff}}` - Typeset an input file with equations to PDF using the [me] macro package: `eqn -T {{pdf}} {{path/to/input.eqn}} | groff -{{me}} -T {{pdf}} > {{path/to/output.pdf}}`