Hi everyone. I have an
issue – My dwg file has become damaged and  I get an error: Drawing
file is not valid. Any
idea? Maybe there is some way to recover it…Thanks

Did it become damaged as a result of AutoCAD crashing?Do you have a .BAK file for this drawing?Did you search for a .SV$ file?Usually the error means the drawing is beyond use but you can try the following.1. Use the RECOVER command.2. Attempt to INSERT the drawing into a new, clean drawing.
John Connor2015-02-06 18:18:38

Open a blank DWG and run the INSERT command. Select the problematic file
and see if it will insert. If it does, then run EXPLODE and select the inserted
block. Run AUDIT and PURGE commands, and then use SAVEAS to create a new DWG.

Look in the same directory where the DWG resides and see if there is a
BAK file of the same name. If so, rename the BAK extension to DWG and see if
the file can then be opened.

Look in C:\Windows\Temp for files with an SV$ extension. If any exist
with a similar name to the corrupted DWG file, then rename the extension to DWG
and see if it can then be opened.

Go to your backup system and restore the file from a time before it
became corrupted.

http://www.filerepairforum.com/forum/cad-tools/cad-tools-aa/dwg/705-how-to-fix-autocad-file maybe this forum can
help