AutoCAD undo information data
File type: 3d graphics, CAD-CAM-CAE file
Files with the ac$ file extension are generally temporary files generated by Autodesk AutoCAD.
They contain temporary working data, including undo information, used during an AutoCAD session.
File type category:
3d graphics, CAD-CAM-CAE file
Date updated: October 12, 2026
The ac$ file extension identifies temporary AutoCAD files. AutoCAD uses these files as temporary working storage for undo information and other session data, including data used when RAM is filled, rather than as permanent drawing files.
These files normally are deleted when AutoCAD closes successfully. If AutoCAD crashes or otherwise closes unexpectedly, an ac$ file may remain in the temporary folder. If AutoCAD is not running, these files can be deleted.
AutoCAD for Microsoft Windows and AutoCAD for Mac use this type of file. It is also associated with AutoCAD AutoSpool on Windows. An ac$ file is an internal temporary file, not a current user-editable drawing format.
The ac$ files are used internally by AutoCAD and are not intended to be opened manually. AutoCAD does not provide a normal editing workflow for these files.
If an ac$ file remains after AutoCAD has closed, it can generally be deleted once no AutoCAD-related program is running. Keep a copy first if recovery of work from an unexpected crash may be necessary.
An ac$ file is temporary undo information, so it cannot be sensibly converted to a standard drawing or exchange format.
Use AutoCAD's supported drawing and export features for conversion of the original drawing instead. Do not rename an ac$ file and expect it to become a usable drawing.
Software apps that create ac$ files:
Microsoft Windows
Apple macOS / Mac OS X
Software applications that handle other tasks involving ac$ files:
Microsoft Windows
Apple macOS / Mac OS X
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