Use sumatrapdf-tool.exe or SumatraPDF.exe with the same arguments.
Available in pre-release 3.7

In the application #

To decrypt a PDF in SumatraPDF:
  • open an encrypted PDF document
  • press Ctrl + K to open the command palette
  • select Decrypt PDF
Or:
  • open an encrypted PDF document
  • right-click to open the context menu
  • select Document > Decrypt PDF

From the command line #

To decrypt a PDF using SumatraPDF from the command line:
sumatrapdf-tool clean -D -p pwd foo-encrypted.pdf foo-decrypted.pdf
Flags:
  • -D : decrypt
  • -p <pwd> : provide password
You can see all flags.
You can also encrypt a PDF.