Thanks both of you for your suggestions. First I've tried to the PDF to EPUB to MOBI to EPUB sequence but unfortunately this didn't help, the page error on the reader remained. Then I tried PDF to TXT to MOBI to EPUB and this gave the desired result in one of the three books. I can read it now on the Sony although the formatting is not "optimal". Perhaps this came about because I wasn't able to find out in the "Convert books" options what user_non meant with "use either textile or markdown output so you don't lose too much formatting".
Any other suggestions to get these PDF's up and running or does this result mean that for these files its simply not possible?