lpf is undocumented. At a minimum it should have the following
lpf -w[width] -l[length]
lpf is an output filter for use with lpd. Document boundaries
are often indicated using the sequence "\031\1". The output
filter MUST put itself to sleep when this occurs
(kill(getpid(),SIGSTOP);) or lpd will hang.
Currently, there's nothing to prevent this sequence from
occuring in a document, so lpf might hang.