Sumatra PDF is a PDF, ePub, MOBI, CHM, XPS, DjVu, CBZ, CBR reader for Windows

Command -register-for-pdf (register SumatraPDF as the default PDF) not working

Using Windows 10 64 I’can’t register SumatraPDF 3.2 as the default PDF from command line with

The command functioned well in Win XP 7 & 8
Windows 10 will not allow you to use that method (afaik, but I have not tried to force it recently)
Windows 10 expects Edge to be the Default PDF reader and persuading it to not do so has been a to and fro battle which varies per release

I install on Windows 10 without that option
Then kick windows in the shins by selecting a pdf and telling associations
its my fervent wish it allows SumattraPDf to open similar such files


Windows 10 doesn’t allow programs to do it themselves (unlike earlier versions).

You have to do it as described at

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The following also works for me equally well:


Is it possible to gray out the ‘Make SumatraPDF my default PDF reader’ option in the SumatraPDF Options Dialog box on systems running Windows 10?

Now clicking that button results in … changing the default PDF viewer from Adobe Reader to Microsoft Edge.

Or maybe better: not gray out the button but launch the online How To docs page instead of editing the registry:

The ‘SetUserFTA’ tool seems to be able to put a specified tool as the default program in Windows 10 by setting the necessary registry hashes (

There are ways to force association without the hash but messing with thousands of users registry entries is considered bad form, especially if the user may not be the pc owner.

If the user is telling SumatraPDF to attempt to be default they should not be surprised if any other default is removed, the wrinkle is that MicroSoft returns it to Edge by default.

For now the best advice is for the user to then manually reassert association with SumatraPDF.

I agree that messing with Windows 10 app assoc registery hashes is not a good practice.
But maybe graying out the button or using the button to open the web page is a more safe & user friendly suggestion.