This article is from the Where to get the latest PGP FAQ, by Michael Paul Johnson email@example.com with numerous contributions by others.
PGP can do conventional encryption only of a file (-c) option, but you
might want to investigate some of the other alternatives if you do this
Alternatives include Atbash2 for DOS, DLOCK2 for DOS & UNIX, Curve
Encrypt (for the Mac), HPACK (many platforms), and a few others.
Atbash2 is interesting in that it generates ciphertext that can be read
over the telephone or sent by Morse code. DLOCK2 is a no-frills strong
encryption program with complete source code. Curve Encrypt has certain
user-friendliness advantages. HPACK is an archiver (like ZIP or ARC),
but with strong encryption. A couple of starting points for your search