When reading MIME messages, Pine uses a mailcap file to determine how to display message parts. Mailcap files are described in RFC 1524, a copy of which can be found as PMDF_ROOT:[DOC.RFC]RFC1524. Or see Section 7.3.5 which gives a brief overview of mailcap files.
The default mailcap filename is MAILCAP. in the PMDF_INIT directory, unless the logical name PMDF_MAILCAP_DIR is defined, in which case the list of directories defined by PMDF_MAILCAP_DIR is searched for the file MAILCAP., in the order listed. The first entry found in the list of files will be used. For instance, with the following PMDF_MAILCAP_DIR definition, PMDF will use a user's own mailcap file, if they have one, and if the user does not have a personal mailcap file, PMDF will use a mailcap file in the PMDF table directory:
$ DEFINE/SYSTEM PMDF_MAILCAP_DIR PMDF_INIT:,PMDF_TABLE:
Note that a trailing colon is necessary if logical names are used because the filename MAILCAP. is appended to whatever value you have specified.