Obtain means to get something that is not so easy to come by such as knowledge, rights, or a large amount of money. You wouldn't say you obtained a pair of pants, unless they were one of a kind.
At times in its history, obtain has meant to be victorious or to succeed. Today, it mostly means to acquire, but keeping its prior meanings in mind helps you to use it in the right way. College degrees are something that you obtain as is permission from your parents to go to a party. When you obtain something, you have worked hard to get it, so you are pretty happy to have it.