Yep, I started using DOORS back when it was Telelogic DOORS, in the late 1990's and the first version I used was 4.2, although the current version (9.7 at the time of writing) really hasn't changed much. Eventually everyone will change to its successor, DOORS NG (New Generation), but we're not there yet.
Maybe I'd better back up a bit. IBM will tell you that DOORS is used for Requirements Management, which is true, but misses what I believe is the real reason - that what we do with DOORS is to use it for the Systems Engineering "V" diagram. More on both of those concepts later.
I don't claim to be a DOORS expert, but I've used it enough over the years that I was taught a lot, and figured out some more for myself, yet I'm still surprised by how much of what I understood to be standard practice still isn't either in the manuals or taught anywhere that I can find. There are plenty of DOORS questions asked & ansered on StackOverflow, many more on the IBM forum, and there's a fair amount written up in the IBM Getting Started and IBM KnowledgeBase. What I've tried to assemble on the following pages is what I discovered that needed to know myself, but couldn't readily find. It is here as much so that I can re-read it myself as in the hope that it may be of use to others.
Much of what is here is about the DOORS scripting language, DXL. It seems there is a reasonable consensus that its documentation isn't great - yes, the DXL language manual does define every function accurately, but you won't find much "how to" information there. Much is in the KnowledgeBase but it seems to require a Google search to find it.