Thursday, August 25, 2011

What Can You Do If You Have Lost Your PDF File's Password? Is There a Way to Remove the Password?

By: Trevor Johnson

Have you ever had an experience where you lost the password to your PDF file and were in desperate need of it again? Maybe you were heading out of town and needed to print a document to take with you but were unable to print it because you had lost the password. Or maybe a colleague at work had decided to password protect a file and they were uncontactable when you needed to open it. Or a company you work with has sent you a password protected PDF but neglected to tell you the code necessary to open it. Which, of course, you don't discover until after the switchboard has closed for the weekend and you need to examine the file before everything opens again.

You may find yourself in a situation like this someday if you have not already. In times like these you must remove the lost password either by hand - which can work if you have an inkling of the password likely to have been used - or by using certain tools.

Fortunately, help is at hand in the form of software. A lost PDF password is actually quite a common event. Any number of reasons can cause you to be in the situation where you can't remember the password that was set, even if it was you who set it in the first place - which can be quite embarrassing.

Most PDF password recovery programs work by first using a set of common words. This is called a dictionary attack and providing one of the words in the dictionary you're using was used to protect the PDF, the recovery will take a very short time. Some programs come with a free trial that will show you part of the password recovered but won't reveal the whole set of characters until you purchase the program.

The better programs will also allow you to use a partial phrase. So if you know that your colleague almost always uses their son's name in their passwords, you can give the program a head start in cracking open the password protection.

If neither of those approaches work, you're in for a slightly longer wait. The last resort of PDF password removal is called a brute force attack. The program will work its way through every possible combination of passwords until it finds the one that will open the file.

If you're certain that the person who password protected the file originally only used letters or letters and numbers, you can usually restrict the brute force attack to that. If they were more security conscious, then you can switch on things like special characters. It should go without saying that it's better not to switch this option on unless you absolutely have to because it will increase the combination of possible passwords and therefore increase the amount of time that it takes to find and then remove the password.

Oh, and just as a side note to dispel a specific rumor circulating around: using these programs is not illegal if the program is used correctly.