How to remove password protect from pdf

I am a student of University.I pay $85 for each of my ebooks and have my UoP password and username to open them.
The problem is that I want to move them to my kindle dx which does not support the password part of the pdf file.How can I remove the password protect from this file.Each page is password protected, but I only have to put in my password one time and it opens the whole ebook.However, on the kindle dx, the cursor does not go to the username or password box, so i can’t open it on my kindle.I tried buying and using a PDF restrictions remover but all it does is say “Restrictions Removed” but the password protect is still on when I transfer it to the kindle.
Any suggestions of what product to use or what to do?
Pls help!!!
Thank you so much in advance.

You should contact the publisher to ask about a compatible versions for your reader and if they don’t offer one, consider purchasing a different format, or potentially working with them to help them provide it.

Cracking an IP protection system, even if you have a license, is not something we discuss here.

If you have forgotten the password of your password protected pdf file them I am afraid to say that you have no way to recover it; but I am not sure that may be some tools available in the internet so called pdf password barker (something like this) could work.

Any tricky ways to remove password protection from a PDF? I just want to copy and paste some stuff from the PDF into notes… I can’t even bookmark the stupid thing… I do not know the password - just wanted to know if there was a way to “hack” it?

Yes - you need to keep a copy of the original on your computer before you apply password protection to it for distribution. The whole point in applying password protection is that other people you distribute your PDF to are NOT able to remove that password protection and so cannot use your content in ways you didn’t authorise.