I don’t quite understand where you get this message? When editing a page in the backend? Can you provide a screenshot of this? See: https://wordpress.org/support/forum-user-guide/block-editor/#adding-screenshots
I also see that your page is currently not being built in the frontend. The output of the HTML code simply stops in the middle of the output of an image. This looks to me like a server-side error whose cause should be visible in your hosting’s error log. I would recommend that you take a look there, your hoster’s support can help.
Yes when making changes to the back end, when I hit ‘update’ to save I get a screen with the message “Validation failed: Upload PDF value is required” or “Validation failed: File Pdf is required”
That is very strange. Which editor are you working with? You are welcome to show a screenshot of this as well as the error message. See: https://wordpress.org/support/forum-user-guide/block-editor/#adding-screenshots
Classic editor. There is a plugin installed so they can still use it. I deactivated it and that got rid of the error message but it still didn’t save most of the changes or make the page content visible.
I would recommend deactivating all plugins. One of them will be responsible for this and also for the text of this error message. If it works without all plugins, you can reactivate them individually to see which one is to blame.
If it still does not work without all plugins, change the theme to a standard theme as a test.
A look under Tools > Site Health can also be helpful.