Have you ever gotten drawings from another company and they were enormous files for no discernible reason? Last week we had a client who was having strange problems with a whole lot of drawings. I enlisted the help of our Civil 3D instructor, Ken Martinez, and he showed me the difference between the typing in "purge" or "-purge" at the command line, as the only way to get rid of RegApps. You have a lot more control with "-purge".
Then just today, as a "Oh, by the way" comment today, Ken showed me this new Cleanup Utility on the Autodesk website, and I thought I ought to pass this along to you. I'm always looking for ways to eliminate headaches.
With this new Cleanup Utility, you can do a batch of drawings at once. Here's the link to the Autodesk page:
Excess Unreferenced RegApp IDs
RegApp Cleanup Utility
I did a little tiny bit of research, and found a good entry in the AUGI archives from 2006 that spells out better than I would how to use the purge command to get rid of invisible attached data from a drawing. It explains how it gets there and how to get rid of it. I copied the entry, (it's from 2006) and also credited the author. For cleaning up one or a few drawings, it's really easy.
From the AUGI website, in the Archives from 2006, is this tip on how to get rid of Xdata in a drawing. Written by Andy Manninen: (and I quote)
I would recommend to all AutoCAD users to run a -PURGE command, then select RegApps, * for all, and no to verify names. You may be surprised at what you will find... Regapps are added when you use certain software, and by implementing certain commands. If you purge these out you will find that your drawings will open much faster. I have not experienced any problems with purging the RegApps out because AutoCAD will generate these back as it needs them. With a clean drawing I have about 8 RegApps in my drawing. But I Have cleaned some that have around 157,000 RegApps. Cleaning that file, the size went from 3 MB to 400KB. The Main thing with RegApps in a drawing is that they act almost like a virus, if you xref in or insert an "infected" drawing, the RegApps propagate into the current drawing. That is why you need to make sure when you get files from an outside source you really should clean out the RegApps. The only way to clean these out without third party software is by using the "-PURGE" command on the command line, (not through PURGE) and you need to specify RegApps. (RegApps are NOT purged under the ALL).