When I click on a specific file, Windows 10 opens a lot of files. Not only the chosen files… And I see up one hundred (or more) of opened files…
What to do ?
Home / Reading PDF files
If tab history is on and you did not close the tabs then they will be reopened next time.
Hundreds seems extreme and will of course slow down opening more, if you wish to keep some and not others, then just close those tabs you no longer want next time. If you want to clear the history uncheck that box close and reopen SumatraPDF.