When word-processing, is there a keyboard shortcut (in MS Word or LibreOffice Writer) to move to the top of the current page in the document? For example, if the cursor is midway down page 3, is there a shortcut that will bring the cursor to the start of page 3?
Different programs have different shortcut keys.
In MS Word, Ctrl+Page Up will move your cursor to the top of the previous page (Source1).
In LibreOffice, Ctrl+Page Up will switch cursor between text and header (Source2). For LibreOffice, I was unable to find a shortcut that moves it exactly to the top of the page, but your comment states that pressing Ctrl+Page Up twice works.