The PDF file format allows for the PDF file to be password protected.

As with every password protection system, the difficulty of cracking the password will depend on several factors:

• Which version of Adobe Acrobat software was used to create the file in the first place. As with most software, earlier versions aren't as secure as newer ones.


• How good the person protecting the PDF was at choosing a password. If they use something simple like "password" or their child's name, finding the lost PDF password is fairly easy. If the password was generated randomly then it will likely be more difficult to crack.


• How long the password was. Shorter passwords are almost always easier to crack than longer ones.

The two main password cracking methods used by PDF password recovery software are called a dictionary attack and brute force.

A dictionary password attack does exactly what it says. It uses a dictionary of words and goes through them, seeing whether any open the file. The bigger the dictionary, the better the chance of success.

A brute force password attack is the computer equivalent of using a crowbar to open a padlock. The success of this method depends on how long the password is. For instance, the 4 digit PIN number that protects your bank cash card only has 10,000 possible combinations, some of which aren't allowed anyway (such as all 4 digits the same). It's more secure because most ATMs will only allow a handful of guesses at the PIN before they swallow your card.

A long password is more difficult for a brute force attack to find. It will find it eventually, but the time taken will depend on the computer power being used and what combination of letters, numbers and other characters was used for the password.

Incidentally, if you want to generate a difficult password to crack, use this free random password generator. Of course, you'll need somewhere more secure than a Post-It note stuck to your screen to store your new, secure password, but that's another story!

There are several PDF password recovery programs available, but the one I've found to be the best is PDF Password Recovery. It's affordable, available for instant download and - most important - it actually works.