But a PDF doesn't have to be A4/Letter. I published a book recently (ebook in PDF, ePub and mobi and paperback) and decided to use 6.69 x 9.61 inches for the PD

But a PDF doesn't have to be A4/Letter. I published a book recently (ebook in PDF, ePub and mobi and paperback) and decided to use 6.69 x 9.61 inches for the PDF. I found that this size looks good on paper and on screen.