I answered in your other thread -->
https://www.mobileread.com/forums/sho...d.php?p=469160 <-- and there are several other answers there as well.
PDFs are most often designed to fit a particular size of paper. Even if the book is printed on non-standard paper, the PDF version may be sized for US letter-sized or international A4-sized paper with wide margins. So, when you put a PDF file on the Sony reader, it's highly likely that it is going to try and fit the 8.5x11 inch image onto the 3.5x5 inch screen. Some PDF files respond well to the Sony's resize function, though I've not had one reflow properly.
You can also run the PDF file through software such as Calibre or MobiPocket Creator and get a better version which can be put onto the reader. I ran a quick experiment with
Pendragon: The Merchant of Death which Barnes and Noble gave away earlier this month. The PDF was OK, but not good on the Sony reader. Running it through Calibre produced a version with better reflow, but it didn't automatically detect the chapters and it retained the header and trailer text from each page. I could easily open the ePub format produced by Calibre and edit it to fix these problems -- but I didn't need to after Amazon released the book as a free download.
Tell you what ... I'll get a couple of photos/scans of the screens & you can decide for yourself.