If you don’t want to save changes you made to your document since you opened or last saved it, you can undo the changes.
To undo your most recent change, choose Edit > Undo.
To undo multiple changes, choose Edit > Undo multiple times. You can undo any changes you made since opening the document or reverting to the last saved version.
To undo one or more Edit > Undo operations, choose Edit > Redo one or more times.
If you’re using OS X Lion (v10.7) or later, you can revert to previously saved versions of your document. To learn how, see Finding an Archived Version of a Document.
If you’re using Mac OS X v10.6 (Snow Leopard) or earlier, you can undo all changes you made since the last time you saved your document, by choosing File > “Revert to Saved,” and then clicking Revert.