I just googled on this topic out of curiosity, and I didn't find anything. Perl2Exe, being rather proprietary, isn't going to be documented in terms of how it works...of course, it IS possible (can you read decompiled assembler?) but it's not going to be fun, and I don't think you are guaranteed to get the original source back exactly as you want it. You'd have better luck if it was made by PAR, but even then, I'm not sure it would result in readable code.
What diotalevi says above is correct...but that's assuming you can get Perl source out of it. If that source is somehow encoded in something non-trivial (i.e. not ROT13 or BASE64 or something like that), you may have a hard time getting something to feed to the DeParser. Start by trying to extract the strings from the executable (look at a hexeditor to see if they are there, or try 'strings') -- hopefully you will see something that looks like Perl code, but probably not.