I got hit with a curveball the other day. A client phoned in to complain that his AutoCAD file was misbehaving and that it was constantly freezing. I went through the usual time-tested process. Copied the file, audited it, purged the living daylights out of the file a bunch of times to get rid of everything that could be gotten rid of. No improvement. So, then I went at all the blocks and did another repeated purge. Yet for love or money, the file would not behave.
Turns out there are many reasons why a file may become slow, but one stood out (it turned out to be the problem in this case as well): Xrefs that were missing.

In Revit, if the links are not found, no problem. The software just carries on working without a problem. Not so much in AutoCAD.
If you are handed drawings with Xrefs, I strongly suggest you either reference them in or get rid of them.

Of course, if fixing the Xref problem does not do the trick, there are some more things you can try. Investigate if the hardware you are running is up to handling the drawing. Make sure there are no network issues if you are working off a server.
Here is a more detailed article on most of the things you can try to make working with the drawing easier.
If you need help with managing your AutoCAD drawings, please contact Micrographics so we may be of assistance.
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