# remove PDF password
# decreptying PDF password
# install any of below software on Linux (Ubuntu) & try below steps.

# qpdf
sudo apt-get install qpdf
qpdf --password=password --decrypt input.pdf output_decrept.pdf


# pdftops
sudo apt-get install xpdf-utils
pdftops -upw password input.pdf

# u will get .pdf file--convert .ps to .pdf
ps2pdf input.ps output.pdf


# pdftk
sudo apt-get install pdftk
pdftk secured.pdf input_pw password output unsecured.pdf