ref: https://superuser.com/questions/179064/how-to-remove-security-from-a-pdf-file
Download qpdf binaries from https://github.com/qpdf/qpdf/releases
qpdf-*-bin-msvc32.zip
and extract
qpdf --decrypt InputFile.pdf OutputFile.pdf
qpdf --decrypt --password=yourpassword InputFile OutputFile
Written with StackEdit.