ZDoom

how to modify a wad and make an "all in one"  (complete edition) like a wad with several chapters inside like The Ultimate Doom which has in it Knee-Deep in the Dead, The Shores of Hell, Inferno, Thy Flesh Consumed
https://i115.fastpic.org/big/2021/0823/ ... 62613d.jpg

I wanted to add/merge 2 in one wads *the first and its sequel into one 

sorry for my english

The pictured WAD was created with a program called WadSmoosh that combines the original first-party Doom IWADs and PWADs into one game. You can download that here:
https://jp.itch.io/wadsmoosh

If you want to do something similar on your own with non-commercial WADs, you'll need to manually do something similar in SLADE. I highly advise that you open up doom_complete.pk3 (the file created by WadSmoosh) and take a look.

Another thing, this should probably go in the base Doom Editing Help forum, not here. This forum is for complete tutorials, not questions.