How to remove the password from a PDF?

I have a password protected PDF file. I know the password but in order to share the file, I have to remove the password from the PDF and share an unprotected copy. How can I do this in Ubuntu with or without the GUI?

The easiest way GUI (recommended for novice)

Open the protected file and use ctrl+p or use print option to print the file, now save the file as pdf.

Using Command line

If you have pdftk already installed you can skip step1

Step 0: To check if Pdftk is already installed

sudo apt list | grep pdftk 

If output contains '[installed]' tag with pdftk then you can skip step1 i.e if the output is like this

pdftk/xenial 2.02-4 amd64 [installed]

Step 1: Install pdftk

sudo apt-get install pdftk

Step 2: Run following command

pdftk /path/to/input.pdf input_pw <yourpassword> output out.pdf

To use qpdf for generating unsecured pdf run following command.

qpdf -password=<your-password> -decrypt /path/to/secured.pdf out.pdf

For detailed information take a look at this HTG tutorial

I tried this in ubuntu mate 19.04:

sudo apt-get install qpdf
qpdf --password=YOURPASSWORD-HERE --decrypt input.pdf output.pdf

Source

sudo apt-get install pdftk
pdftk input.pdf output output.pdf user_pw YOURPASSWORD-HERE

This takes your input.pdf, removes the passwords and exports it as output.pdf.

You may want to take a look here to explore additional mehods.

Rising the topic from the dead a little bit here (but I am a new Linux user, so...);

1. Anyhow, I also used the file for which I had known the password. But I used "Master PDF Editor 5" (unregistered, free version) to remove the password (File - Properties - Security - No Encription).
2. However, since "Master PDF Editor 5" leaves the watermark (which I personally, do not mind), I re-opened (the now unlocked file) in Libre Office Draw and removed the watermark.
3. I exported the file in PDF, which additionally resulted in tremendous compression without any losses. It was a very simple file; one sheet only, with text in the table, but the above process reduced the size from 70-ish KB to 22-ish KB.