Hello,
I couldn't make the protocol work in the registry for context menu items - eventually I found a solution I'd done on a previous computer and copied it -so I can't acknowledge those who provided the original info, but I couldn't find anything on an extensive internet search today, so here goes:
To set the Windows Store version of Paint.Net as a context menu "Edit with PAINT.NET" use the registry entries below. To make it the default "edit" just change delete the "..with PAINT.NET" from both keys below and import to the registry:
[HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Edit with PAINT.NET]
"AppUserModelID"="dotPDNLLC.paint.net_h55e3w7q8jbva!dotPDNLLC.paint.net"
"PackageRelativeExecutable"="PaintDotNet.exe"
"Parameters"="\"%1\""
"ContractId"="Windows.File"
"DesiredInitialViewState"=dword:00000000
"PackageId"="dotPDNLLC.paint.net_4.200.7133.0_x64__h55e3w7q8jbva"
[HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Edit with PAINT.NET\command]
"DelegateExecute"="{BFEC0C93-0B7D-4F2C-B09C-AFFFC4BDAE78}"
Hope that helps anyone who is still looking for this.
