DOOM2.EXE

DOOM2.EXE is the main executable for the original DOS versions of Doom II and Final Doom.

Latest version of Doom II
Version 1.9 is 709905 bytes in size. It has the following hashes:

Final Doom
The executables distributed with the DOS version of Final Doom were both also named DOOM2.EXE. They are both identical. The name displayed when running them depends on what IWAD the executable detects on invocation.

Despite some significant differences from the DOOM2.EXE provided with Doom II, Final Doom's 'DOOM2.EXE'' claims to be version 1.9.

Pirated versions
A number of pirated versions of doom modified the files in some way. In order to prevent these from being useful, a number of ID and non-ID tools attempt to detect well-known stolen copies.

Dehacked
The Dehacked EXE-editing tool will display the following message if DOOM2.EXE file is 686921 bytes in length:

Using Doom 2 v1.666 You are not using a legal copy of Doom. This copy (created on 8/25/94) was stolen from Id and spread widely by software pirating groups. This is a lame way to have fun at the expense of a cool company like Id. Buy a legal copy of Doom today!

Dehacked will then pause for 180 clock-ticks. The length of a clock-tick depends on the operating system and processor: POSIX defines the value to be 1000000 clock ticks per second.

ID's PATCH.EXE
The official patching method supplied by ID Software will refuse to operate if it detects what it thinks is a pirated copy of Doom 2.

According to doomworld, the doom2p PATCH.EXE variant will not operate on a version of Doom 2 dated 1994-25-08, as this version is declared pirated.