By default, when you undo a step using Edit > Undo or the History panel, the file size of the document does not change, even if you delete an item in the document. For example, if you import a video file into a document, and undo the import, the file size of the document still includes the size of the video file. Any items that you delete from a document when performing an Undo command are preserved to restore the items with a Redo command. To permanently remove the deleted items from the document, and reduce the document file size, select File > Save And Compact.