How can I restore my iPad from iOS 5 to iOS 4?
iTunes will not willingly load a lower iOS onto a device. Have you looked into the tiny umbrella program to see alternate methods to trick iTunes into doing what you wish. 

iOS 4 requires an shsh key to sign the 4.3.3 package for your specific device. This key normally comes from the itunes actication servers. Unless you have already saved that key, the automation tools won't work and you'll have to do muh deeper hacking to crack this nut. 



tl;dr 


read up on jail breaking
it might be too late for you to go back easily