If you have the Postscript processor Ghostscript/GSView installed you can open the pdf in that and ouput pages in various graphics formats - bmp, ps, jpeg, png etc. You can then use a standard graphics program to read the graphics file in and add text. (And if you want to convert it back to pdf you can print it out using something like PDFWriter as a vitual printer that created pdfs. These are both free.

There are also free toolkits that let you manipulate pdf files - have a look at xpdf and pdfToolkit, which I think can both convert pdf files to postscript that you can edit in a graphics package.

When I converted the DT to abc format, I added the option to output notes at the bottom of the text and this I did in the way Joe suggested in the last post - (mis)use the lyrics W: tag and write the notes on there, putting them after the proper lyrics with some blank W: to separate them. I was using abcm2ps to generate postscript files from them, but if abcNavigator can output lyrics it should do the same thing. Ideally it would be nice if you could specify that the program could optionally print the N: tags out, then you could have the notes properly on N: but still be able to print them with the tune, but I don't think any of the packages have the option (although it would be trivial to implement).

Mick