Is a contract valid if all information is not presented before a contract is signed?

That depends.  Was the information material?  A failure to disclose unimportant information is not fraud, and will not invalidate the contract.  If the person selling you a car failed to disclose that the odometer had been rolled back 40,000 miles it would probably invalidate the contract; if  he neglected to tell you that the odometer had been rolleed back 3 miles, it probably wouldn't. Did the person who knew the information have a duty to disclose it?  As a very general rule, with many exceptions, one is under no duty to tell the other party about information that you know unless is is information that you had special access to (for example, you are probably not obligated to tell a party buying your property that it is only zoned commercial, because that is a matter of public record which they can find out; you probably would be required to tell them that a neighbor had disposed of toxic chemicals on his next door property) or you have made an affirmative representation about the subject matter (for example, if the seller told the buyer that the property was zoned residential, that would probably invalidate the contract, even though they could have found out tot he contrarty by checking). Did the person who was not aware of the information enter into the contract because of that lack of information?  If the person selling you a car failed to tell you that the odometer had been rolled back that would normally invalidate the contract, but you were only buying the car because it had once been owned by Elvis and weren't planning to drive it, you didn't rely on the failure to disclose, and won't be able to invalidate the contract.