pass file is a extension for adding arbitary files to the pass password store. Files will be encoded using base64 before encryption. This extension is inspired by gopass' binary function to which it is also compatible. Files stored with gopass binary can be retrieved with pass file and vice versa.
Usage: pass file action pass-name [path]
Actions:
store|add|attach: add new file to password store
retrieve|show|cat: retrieve file from password store and print it to stdout
Storing a PNG picture and retrieving it.
pass file store pics/secretpic mypicture.png
pass file retrieve pics/secretpic > retrieved-picture.png
Alternativley you can also use shortcuts for attach and retrieve:
pass file add article my_super_secret_revelations.txt
pass file cat article
See here for details. There is also information on how to install extensions in the pass man page.