Can't edit my resume in/with Pages

If your résumé is already in a Word document, I recommend you open/edit/save in MS Word. If it is a PDF, you can open that in MS Word v16.31 or later and convert it to a Word Docx document. Pages cannot open a PDF document.

You can open a Word document in Pages, make your changes, and then export back to Word or PDF. Pages is not a Word clone, so it translates the Word document into Pages internal .pages document format when opening the former document. The Word document remains unchanged. Exporting from Pages back to Word is also a translation process, and the result, when viewed in Word, may not look as you left it in Pages.

There are features in Word and Pages that are not compatible with either application, and the translation process will make this very apparent.