Hello
experts,

I have a
dwg file that is corrupted or encrypted and I need to fix it.

Is there
any tool I can use to check the integrity of the dwg files.

There is a big difference between a corrupted drawing and one that is encrypted.If a drawing is corrupted then try using the RECOVER command to open it.  If the drawing can be opened but not saved for some reason then try using the Overkill, -Purge (Regapps then All) and Audit commands on it to clean it up.  Once you do then maybe, just maybe you can save it but I'd recommend saving it under a different name.If the drawing is encrypted (do you mean password protected?) then kiss it goodbye because you aren't going to open it.  Period.
John Connor2015-11-17 15:39:23

The RECOVER command did not help. the file is not opened.

If the drawing is encrypted by password protection, it will politely ask for a password on open.

Who gave you the drawing?

Maybe a quick check suggested by the principal themselves with various
steps 

http://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/AutoCAD-File-Corruption.html

Otherwise, try using  DWG Recovery
Toolbox s/w just to make the file legitimacy for recovery chances of prev
copies.  http://www.oemailrecovery.com/dwg_recovery.html

Hopefully
from Autocad autosave by default, it should have saved dwg file automatically
with ac$ as default extension, and if we can just find the *.ac$ file and
change ac$ to dwg. There may be slight chance. The AutoCAD's autosave file is
saved in this folder: C:\Users\[User Name]\appdata\local\temp\. typically.

Look at it this resource. Perhaps you will find there
more useful information.

http://www.instructables.com/answers/Autocad-CorruptInvalid-File/

diego: Attach a copy of the drawing to your next post.  Maybe someone here will have better luck unless of course it is encrypted in which case neither you nor anyone else here will be able to open it without the password.

Thank you guys for your feedback and help. Sorry, that long time did not respond. This is because the issue was solved and I forgot to tell.) Thank you!