Which option should I pick?
“Same layout, editable” for forms, letters and invoices: every line stays where it was, with its font, size, colour and boldness, and lines, boxes and pictures sit behind the text. Each paragraph is its own box: edited words rewrap inside it as they do in Word, and a much longer edit grows the box downwards. “Flowing text” when you will rewrite a lot: you get real headings, paragraphs, lists and tables that reflow. “Page pictures” keeps every page as a picture you cannot edit.