I underline things in the pages with the document markup red underline tool. I save the page.pdf
Then I create a document from many pages underlined. If I need to swap out a page for another, the page is goine but the red line comments stay where they are and need to be deleted. Is there a way to create a page where the red underlines are locked on the page, and then if the page is replaced with another, those lines go away with the page... so you don't need to delete them and they aren't just hanging around on the new page, separate from the one they were originally put on?
Oftentimes the behavior you are describing is actually beneficial: You can replace the page content, but all your annotations and form fields remain in place. This allows you to easily update e.g. the background of a form, and you don't have to recreate the form from scratch.
When you replace a page, that is the behavior you get. In order to also remove the annotations, delete the page first, and then insert the new page in the location you want it to appear within the document. Deleting a page will remove the annotations that are associated with that page.