PDF scan is relatively better (than the JPG scan). But even there, the white spaces especially on the margin can overwhelm the eye. So is applied the next technology of OCR — Optical Character Recognition.
Through OCR applied on the paper book pages (or their JPG scans) the entire text can be converted back into a SOFT-COPY.
Which, in turn, can be adjusted with bigger FONT sizes & lesser MARGIN widths. In order to reduce the white lights (glare) coming from the screen. Thus when the adjusted OCR is finally presented as a PDF file, it becomes unusually soothing to read in the screen world.
This modern technology OCR is so amazing that BOTH the Pirates & the Google, opt for it in their book-scanning works.