PDFs can be scanned just as easily as paper documents, as long as you have the right software. This could be a great option if you have OCR software installed, and could prove a much better option than one of the hit and miss PDF converters discussed above.
Various free OCR tools are available for Mac OS X, so you shouldn’t have much trouble finding a useful solution.
On a related note, when creating PDFs by any of the methods discussed here, you may find that the file isn’t correctly created if you don’t have the right fonts installed on your Mac. While this shouldn’t happen (PDF doesn’t rely on fonts for reading) it could result in people being unable to read the document. Fortunately there are ways around this problem.