Frankly, I wouldn't bother with pdfs and instead make cbz or cbr files. You need CDisplay to view those, but all you'd need to do is pop all the images into a zip or rar file and change the file extension to cbz (zip) or cbr (rar).
e: But if you're set on pdfs,
check this out. It's a tutorial to convert cbz into pdfs but if you already have all the files in one folder you can just skip steps 1 and 2. (Although if you could also make a cbz or cbr while you're at it, that would be great!)
Also, there are a few pdfs already
floating around, so you may want to save yourself the work and stick to those that haven't been collected yet.