After much experimentation, I am of the opinion that the pdf file format should be used only as a last resort.
If you possibly can, convert the pdf to html and then to epub. Strip out unnecessary images. These make sensible conversion more difficult.
If it is a scanned file that for some reason you cannot OCR, reduce the pdf to a series of jpgs, zip them up, change the suffix to cbz and convert to epub in calibre. You can then view in landscape and the file will use the whole page.