Inventor - Open Inventor files in active instance
March 22, 2022 By Florentina Stirbu
A common issue for Inventor users is that opening an Inventor file from Vault or Windows Explorer will launch a new instance of Inventor, even if there is one already running.
Most likely this is because the Inventor version is not correctly registered for the corresponding file types.
For all affected Inventor file types except .DWG, follow the steps below:
Browse to a file of the corresponding file type in Windows Explorer (or get it from Vault then go to the Working Folder).
Right click file -> Open with ...
Check the "Always use this app to open *.* file" box.
Select Autodesk Inventor 20xx.

If that doesn't help, try re-registering Inventor using the Command Prompt. Instructions are available here.
As .DWG is a file extension that can be opened both in Inventor and AutoCAD, it must use the DWG launcher, which means that when a .DWG file is opened, the launcher determines whether it should be opened in Inventor or AutoCAD.
Right click a .DWG file in Windows Explorer -> Properties
On the General tab, next to "Opens with.." select "Change".
Locate "AutoCAD DWG launcher in that list -> OK

In the current Inventor session, open a DWG. All future DWGs should then open in the same session.
Editing the registry is not needed in most cases. However, if the problem persists, consider modifying the registry keys as advised here.