I tried to make an easy solution in Automator, but couldn't get everything to work together.
The command line has a utility called 'say' which will convert text to speech using the built-in voices. By default, it uses the selected voice in System Prefs, but you can specify another.
While Automator's PDF to Text utility works fine, Say wants a UTF-8 encoded text file. I couldn't find a way to make that work with Automator's output.
There is a nice pdf utility you can install that will convert pdf to text and allow you to set the encoding. The [xpdf-tools-3.dmg package is here|http://users.phg-online.de/tk/MOSXS>, at the bottom of the list of files. Once installed, you can use one of the utilities, pdftotext, to convert the pdfs to text, and then use say to convert the text to an m4a file.
To convert the file to text use:
pdftotext -enc "UTF-8" <path/to/file.pdf>
You can optionally add the output file after the pdf. You can also specify the first and last pages with -f # and -l #.
For say, use
say -o <path/to/outputfile.m4a> -f <path/to/file.txt>
The documentation states that output tile format is only available in 10.6. If you give the output file a recognizable extension, say will determine the output format from that. So, use .m4a to convert to the AAC codec.
I'm not good at packaging shell scripts into easy to use applications, but perhaps with the above, someone else can put it all together into a droppable application. However, the nice part about doing it in steps is that you can edit the text file to get rid of any extraneous things that might make it less intelligible.
