Before Win 10 you can just use Settings/Options menu at any
time.
In Win 10 it's more complicated. You can try the following
methods.
- Right-click SumatraPDF.exe in
c:\Program Files\SumatraPDF
(orc:\Program Files (x86)\SumatraPDF
) and select Run as Administrator. - Go to
Settings > Options
and click the button to set Sumatra as the default PDF viewer. - Close the program.
If issue is still not solved:
- In file explorer, right-click any
PDF > Open with > Choose another app
. - Check the Always use this app to open .pdf files checkbox.
- Scroll down and click on the More apps ↓ link, then select SumatraPDF from the list and click on the OK button.
- If SumatraPDF is not in the list, scroll down and click on the Look for another app on this PC link.
- In the Open with… dialog navigate to
c:\Program Files\SumatraPDF
(orc:\Program Files (x86)\SumatraPDF
), select SumatraPDF.exe and click on the Open button. - The PDF should open with Sumatra, and all PDFs when subsequently double-clicked should open with Sumatra too.
If issue is still not solved:
- Open Settings app.
- Go to
System > Default
apps. - Scroll down and click on the Choose default apps by file type link.
- Set SumatraPDF a the default app for the .pdf file type.