How do I force open the super drive? Have a DVD that I can't eject

There's a number of ways but a simple one is boot with the mouse key down.

If it is mounted then drag it to the trash (assuming you have Finder preferences sohow on desktop settings to show it on desktop.

Disk Utility Eject.

Eject key on keyabord.

Pull the door down (finger nail or such) and insert a straightened paper clip into the hole towards the right lower portion of the face of the optical drive. Push with the paper clip and the tray will open enough to allow you to pull it all the way out.

Do you have to pull the aluminum door down from the inside, with the side door off? I can't easily get enough of a grip on it from outside to get it to open. (2009 MacPro 4,1)

Do you have to pull the aluminum door down from the inside, with the side door off? I can't easily get enough of a grip on it from outside to get it to open.

Try a creased business card or such?

metal nail file, letter opener, collection of a lot of small flat screw-drivers and such.

On mine I ended up taping the front door down in down position <take that, optical door>

On startup: use mouse-down position and wait for the system to halt where you should, normally, or it will try to slide open to allow chaning DVDs.

<take that, optical door>

I also find frustration/exasperation often beats finesse......😉

OK, here is one that always gets overlooked. Create a burn folder or drop some data into Toast (if you have it) and press the burn button. The tray should just open without the use of heavy machinery. Then just cancel the burn.

You're wrong I believe. Unless you're talking about a different Mac Pro? I have the 1.1 from 2006 with dual superdrives (Optiarc AD-7170) The upper has been a problem for some time, so I generally used the lower drive.
The paper clip hole is about 2 3/8 inches from the LEFT of the drive--the paper clip physically releases the tray.
There is a large button on the right side also, but that only works when the drive is actually operative, so it's pretty much pointless.
I never realized how easy the DVD combo slipped out from inside the Mac Pro----take the removable side off and the two drives simply pull out sideways. One then has access to entire front of the superdrives and can poke the paper clip in the correct hole and get the stuck DVD out.