I have used the demo version of the program and added a new blank page like you did and then saved the modified file. The software appended DEMO to all the pages, but the last page is blank and it appears normally. Only the watermark is added. I have checked all the other pages in the document and it appears normally. I have also used images, text, and shapes inside the PDF file, but they were not cropped at all. Try reinstalling the software and add the PDF file again.