A requirement of Risen3D is that your iwad is both up to date and unmodified, the official patches are available below.
Both Doom and Doom2 need to be v1.9, the Ultimate Doom patch provides for episode 4.
Doom ( current version 1.9 or Ultimate Doom )
Doom2 ( current version 1.9 )
Note: there is no patch for Doom2 v1.666 dated 8/25/94. This version has been declared "pirated" by id Software and is no longer supported.