The DWG file format is the same for 2007-2009, but if you are using a vertical, then it can be a different story. If your DWG file contains content from your vertical, it may no longer be usable in earlier releases after saving in a later release, regardless of whether DWG file format is the same in both releases, or not.
AcadXTabs: MDI Document Tabs for AutoCAD 2009
Supporting AutoCAD 2000 through 2009
"Gman" <-> wrote in message news:email@example.com...
I searched around but was unable to find the answer.
Is the Acad 2009 dwg file format same as Acad 2008?
Can I open Acad 2009 dwg's in Acad 2008?
Like Tony said, the file version is the same from 07-09... the situation can vary for verticals only because some of their specific more-intelligent objects can change or be improved from release to release, so they may not behave identical from 2009 to 2007 for example.
The same happens for vanilla ACAD... you can create MLEADERS in 2008, 2009, but if you open them in 2006... they won't be the same. Same with dynamic blocks... they aren't the same if you open them before 2005.
Of course Inventor is a whole file type apart from everything (.ipt, .iam) so you really can't compare that to the DWG's Mechanical or ACAD use.