Here is ine response I found on Adobe using your heading
When in Adobe Acrobat 5, I often use the "replace a page". Why does the file size always increase when I do this? I would think the file size would remain the same or close. However, I may start off with a file that is 95kb, and after using the "replace page" a few times, I have a file that is 916kb and still the same number of pages! It is not because the new page I'm replacing with is a larger file size. Why does this happen?