PDF files seem to be almost everywhere nowadays. Most of them can be opened at the click of a button but if they contain sensitive information then there’s a good chance that they will have been password protected. Which is good news if you want to keep your data safe from prying eyes but bad news if the file is legitimately on your hard drive but stubbornly refuses to open until you give it the magic word! Which is where password recovery for a PDF file comes into play.

PDFs are password protected for a variety of reasons.

Sometimes you will have bought a short report and the author will have decided that by password protecting the document they will protect their revenue. They don’t care that this means treating actual buyers like yourself as thieves. And if the file is more than a few months old, the chances of finding the email that held the password are remote. Contacting the author should be possible but of course you need to be able to open the PDF first to be able to find their details. Which is kind of a Catch-22 situation.

Password protected files at work are even worse. Your screen would be covered in Post-It notes if you kept all the separate passwords “securely” taped to it. Keeping a folder with the passwords in it is just as insecure. So you have to find other ways to memorize the passwords.

Which may work, but Murphy’s law says it won’t work when you need it most!

This is where software to help with password recovery for PDF files comes in handy.

Most of the software out there works the same way:

  • Load a dictionary of common words and try these out first. If the person who sent you the password protected PDF wasn’t too paranoid, this will be the quickest way of recovering the missing password.
  • Try every possible combination of letters, numbers and punctuation. Starting with single character passwords and progressing to ever more difficult ones.

This second technique is guaranteed to work. Eventually.

The thing with password protection is that the longer the password protecting the PDF or any other file, the longer it will take to crack it.

It’s a numbers game: the longer the password, the more possible combinations there are.

For instance, the PIN that protects your financial data is only 4 digits long. It only allows numbers, not letters or anything else. Which means there are only 9999 possible combinations. Or actually slightly less as certain combinations aren’t allowed as they are deemed too obvious. This relatively weak security only works because ATM machines will swallow your card after a handful of incorrect attempts.

With a PDF, there’s no such restriction. A computer program would be able to crack a 4 digit password in seconds.

It takes longer for a program to check longer passwords. If you have an inkling of what the password should be, you can reduce the amount of time taken by restricting your software to – say – just letters and numbers. But if not, grab a pot of coffee or even a couch whilst your chosen program goes about the task of recovering the password from your PDF file. It’s do-able. It just may take a while!

Globally Technology

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Thursday, Oct 21, 2021