This article is from the PGP mini FAQ, by Andre Bacard abacard@well.sf.ca.us with numerous contributions by others.
Yes. For example, a document encrypted with PGP on a PC
can be decrypted with someone using PGP on a Unix
machine.
As of September 1, 1994, Versions 2.6 and higher can read
previous versions. However, pre-2.6 versions can no
longer read the newer versions. I strongly recommend that
everyone upgrade to Versions 2.6.2 or 2.7.
 
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