What is QPDF
QPDF is a command-line program that does structural, content-preserving transformations on PDF files. It could have been called something like pdf-to-pdf. It also provides many useful capabilities to developers of PDF-producing software or for people who just want to look at the innards of a PDF file to learn more about how they work.
QPDF is capable of creating linearized (also known as web-optimized) files and encrypted files. It is also capable of converting PDF files with object streams (also known as compressed objects) to files with no compressed objects or to generate object streams from files that don’t have them (or even those that already do). QPDF also supports a special mode designed to allow you to edit the content of PDF files in a text editor. For more details, please see the documentation links below.
Install qpdf on Ubuntu
The qpdf package is also part of other Linux distributions which is useful to crack the pdf file with password.You can install the qpdf by using following command
sudo apt-get update
sudo apt-get install qpdf
go to the pdf file directory first
To unlock the pdf run the following command
qpdf --decrypt pdf-loackedfile.pdf --password=yourpassword unloacked-pdf-file.pdf
pdf-loackedfile.pdf = The file which is password protected
yourpassword = replace with the pdf passsword
unloacked-pdf-file.pdf = the crack pdf file without password