AutoCAD DWG Files unexpectedly increase in file size

Issue: 

Drawing files in AutoCAD end up being much larger than they should, often with no obvious data in them. Other symptoms include failure to copy and paste elements in the drawing, when selecting text with the properties palette open will cause the process to hang for a long time.  

Causes: 
This happens when data is imported from a DGN file and the original linetypes were either incorrectly or not mapped to AutoCAD linetypes. This produces a huge object database in the drawing that cannot be purged with the standard tools. Furthermore, if you copy and paste an entity from the drawing into another drawing, the entire database is also copied, spreading the problem to the new file. 
  
Solution: 
There is a hotfix for AutoCAD to overcome this problem. The Hotfix includes two files:  
The DgnLsPurge.dll, once loaded will allow you to purge these DGN objects. 
The AcDgnLS.dbx is included to keep the DGN objects from propagating to new files when copying, pasting or inserting from other files.

For AutoCAD 2013 / 2014: AutoCAD® DGN Hotfix 
For AutoCAD 2012: AutoCAD® DGN Hotfix for AutoCAD 2012 

For AutoCAD LT: 
Try out the following procedure. 

• Open the file with AutoCAD LT.
• DXFOUT the full file.
• In a new file DXFIN the file created in previous step.
• DXFOUT the full file.
• In a new file DXFIN the file created in previous step.
• Purge all.
• Save the file.

Note: The problem is partially solved with AutoCAD 2014 and AutoCAD LT 2014 with the SP1 (the part to avoid the propagation with the copy and paste), but to clean the file you need to install the hotfix and run the DGNPURGE. 

If you have installed the SP1 for AutoCAD and AutoCAD LT 2014: 

1. Try the following procedure if the previous methods fail: 
2. Open the file.
3. With the LAYER command, assure that all layers are On, Thaw and Unlocked.
4. Copy all objects in the drawing to the Clipboard (CTRL+C).
5. Open a new file and paste all objects (CTRL+V).
6. Save the file.

For Autodesk AutoCAD LT 2013, please follow the following workaround: 

1. Open the affected drawing file using Autodesk AutoCAD LT 2013
2. Enter DGNEXPORT at the command line
3. Select V8 DGN under Files of type and click SAVE
4. When the Export DGN Settings message box is displayed,
5. Verify that the correct seed file and units are selected
6. Click OK
7. After the DGN export is complete, open a new template and enter DGNIMPORT at the command line
8. Select the newly created DGN file and click OPEN
9. Verify that  the Conversion unit is correct
10. Click on Mapping setups and select new and make sure Mapping type is Import
11. On the new Mapping setup, click on Modify…
12. GO to Linetype tab, change all rows to ByLayer (Tip: Right click on the first row which has been set to ByLayer and the select Copy. Select all the Rows>Right click>Paste)
13. Click OK

This document contains content adapted from the Autodesk® Knowledge Network, available under Attribution-NonCommercial-No Derivative Works .