SumatraPDF registers itself for all supported file types (.pdf, .png etc.).
If there are no other applications registered for a given extension, you can open the file in SumatraPDF simply by double-clicking the file in File Explorer.
If there is more than one application, you have to explicitly tell Windows 10 to make SumatraPDF default application.
In File Explorer:
Open with
and then Choose another app
From the list, choose SumatraPDF
and check Always use this app to open .pdf files
:
This is based on latest Windows 11 build at the time of this writing.
Unfortunately the details differ between Windows updates.
Launch Default app
section in settings app, e.g. use Windows logo
hot-key to launch system-wide search, type default apps
and click on Default apps
search result to launch settings app.
In Default apps type .pdf
for file extension:
Click on current default PDF application (Microsoft Edge
in this example) and select SumatraPDF
: