I posted this in the AutoCad mechanical forum, but I had zero attention or possible solutions to it. So I'll repost it here because you guys seem to be pretty on the ball.
"Just a little bit ago, out of nowhere, it seems the default opening program for dxf files suddenly changed. I noticed when I double clicked to open a dxf file, it opened up "DWG TrueView" instead of AutoCad Mechanical like it was. So I changed it back to the way it was. Now, since doing this, the file icons for dwg's and dxf's are exactly the same. Before they were different. I know this sounds like it's not a big deal, but for me it is very annoying, because for years I've been able to easily tell the difference between the two without looking at the file extension. Anybody know how to help me out? Please?"
Sounds like you might have a registry/permissions issue..
What if you log on as a different user (possibly an administrator account)
Well, I am an administrator. Not sure if I can get someone else to allow me to log in however under their user account. I had a response in the autocad mechanical forum, one guy believes I may need to set Autocad DWG launcher as my default, however I cannot seem to figure out the filepath to Autocad DWG launcher, which is frustrating considering it is set as my default for dwg files. Anybody perhaps know the path to this program?
BTW, I'm with you on the PMI. Hurry it up.
Have you tried a repair install on acad mech? That "might" reassociate the extensions properly.. Typically the last program added "can" steal that association