The "The file format is invalid" message typically means that the file you're trying to open is corrupted or damaged. This can happen for various reasons, such as issues with the file transfer, improper saving, or a software malfunction. While this message usually relates to text files, if you're dealing with a video or multimedia file in Pages, it might be worth trying a repair tool to fix the file. One such option is
Clever Online Video Repair, which is a free tool that can help repair corrupted files, including videos, without requiring any software downloads. While primarily used for video files, it’s worth exploring to see if it can help with your issue. If the problem is with a video or multimedia component within your Pages document, Clever Online Video Repair could be a simple, free solution to try