Source: https://dukeworld.com/classic%20dukeworld/tc/quakedmp/qdmpdemo.zip

Steps:
* Unpacked qdmpdemo.zip, short of install.txt and the BAT files.
* Renamed qdmpdemo.con to GAME.CON.
* Unpacked QDMPDEMO.GRP with kextract and then deleted QDMPDEMO.GRP.
* Removed GAME.CON as unpacked from the GRP. Basically the same as the one
from qdmpdemo.zip, but still including DEFS.CON and USER.CON as separate files
and missing an addition to the file's header identifying itself as a part
of qdmpdemo v1.0.
* However, the GRP's DEFS.CON and USER.CON were left in, just in case
of any relevance (e.g., loading one mod on top of another one).
* Created a new archive from the available contents.

On a side-note, qdmpdemo.zip's external GAME.CON file had
an identical copy of DEFS.CON's contents from the GRP. It also
had virtually the exact unmodified contents of the GRP's USER.CON, short
of episodes 2-4's names (the unused CON file had purposed episode names).