By Justin Doughty
I’ve recently seen an issue where multiple versions of Revit are installed, and the file association for Revit seems to get mixed up, or stuck opening with one version. Right click and “Open With” doesn’t see Revit in the list of applications, and the file icons are a generic white image.
There is an easy fix to this issue, by editing the registry.
DISCLAIMER
This article contains information about editing the registry. Before you edit the registry, make sure you understand how to create a backup and restore it if a problem occurs (Microsoft Link), as this can render your system inoperable. You edit the registry at your own risk.
The first step is to edit the windows registry with regedit. Then navigate to one of two locations, this will vary depending on versions of Windows and version of Revit, but you will only have one of these:
Windows 7 and older versions of Revit:
HKEY_CLASSES_ROOT\Applications\Revit.exe\shell\open\command\(Default)
Here you will find the value:
C:\Program Files\Autodesk\Revit 2015\Revit.exe" "%1
Windows 7/Windows 10 and newer versions of Revit:
HKEY_CLASSES_ROOT\Revit.Project\shell\open\command\(Default)
Here you will find the value:
C:\Program Files\Autodesk\Revit 2017\Revit.exe" /dde 
All that needs to be done is make sure this value displays the correct year versions of Revit you are using or wanting to open .rvt files with. If it is incorrect, edit the default key and replace the year with the correct version.
This should now give you the ability to right click and “Open With…” and now select Revit:
