pgpewrap is a program included in the Mutt email client package that has neither a manpage nor --help or -h screens. The only documentation is a brief mention in the PGP-Notes.txt file in the mutt documentation:

This is a little C program which does some command line munging: The first argument is a command to be executed. When pgpewrap encounters a -- (dash-dash) argument, it will interpret the next argument as a prefix which is put in front of all following arguments.

pgpewrap pgpe file -- -r a b c

will execute

pgpe file -r a -r b -r c

This script is needed with PGP 5 and with GPG, since their command line interfaces can't be properly served by mutt's format mechanism.

You need this for multiple recipients because GPG needs -r to for each of them, while Mutt can only output them as a single list, such as key1 key2 key3. pgpewrap is used to fix the command line for GPG so that -- -r key1 key2 key3 becomes -r key1 -r key2 -r key3.