You can try converting them in GIMP or OpenOffice. But graphics intensive PDFs will get quite large; compare, for example, plaintext books online to the scanned PDFs. The latter can easily be 100 times the size of the plaintext.
hmm i had the same problem with files being to big
have you tried any online converters instead? i couldnt get to use them but once i did it was quite a bit more comfortable
basically what iw as trying to do, just like you was to convert many jpgs to one pdf, and for taht there are two sites, firstly you
have to convert the jpgs and once that is done you have to combine the pdfs into one file.
I usually get results with under 10mb for quite a lot of pdfs…
hope this helps