How Do I Use qpdf To Remove The Password?
Type the following command to install the qpdf:
$ sudo apt-get install qpdf
Decrypt a PDF called input.pdf with YOURPASSWORD-HERE password and create unencrypted output.pdf, enter:
qpdf --password=YOURPASSWORD-HERE --decrypt input.pdf output.pdf |
或者 https://pdfio.co/zh/unlock-pdf/