From Palmtop BV Homepage:

1. Download ENCORE 0.20 by clicking here (45k).
2. In the \SYSTEM directory of your Series 5, create a directory \SYSTEM\APPS\ENCORE. You may have to make your SYSTEM directory visible first using the "Preferences" option of your Series 5 system screen.
3. Use PKUNZIP to extract the four files from ENCORE.ZIP and copy them into this directory (e.g. using PsiWin).
4. Create a GAME.WAD (see below) and also copy it to the ENCORE directory.

After this, you will have an ENCORE icon in your "extras" bar. The application offers a HELP option which provides further instructions.

We have developed a DOS application called MAKEGAME.EXE which allows you to play any DOOM level on ENCORE 0.20. You can download it here (22k).
 It works as follows: 
On your PC, run MAKEGAME in the directory of your shareware or commercial version of DOOM to build a new GAME.WAD 
copy this GAME.WAD to your Series 5 "ENCORE" directory (replacing the previous one). play 

Not too complex, we think. If you haven't got DOOM, check the links at the bottom of this page.
If for some reason you can not make your own GAME.WAD (e.g. because you do not have a PC), we've provided a demo file you can download by clicking here (215k).