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

In the application #

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

From the command line #

To decompress a PDF using SumatraPDF from the command line:
sumatrapdf-tool clean -d foo.pdf foo-decompressed.pdf
For an explanation of all flags, see sumatrapdf-tool clean.
You might want to decompress a PDF to inspect its structure more easily.
If a PDF file is compressed, the decompressed version should be bigger.
If a PDF is already decompressed, this will have little effect.
You can also compress a PDF.