Abhin,
Fax servers, as you know, allow you to fax from your PC and fax directly to your PC. Most good Multifunction Printers will include a fax server with it. If you look at them on their site, under specs, you want to look that it is capable of networking and Fax to PC and PC to Fax. You can also look and see if it faxes directly to PDF. Most do. Some only tiff, but those can be converted to PDFs.
There are software programs which work with a modem or fax card such as Snappy Fax and others.
Then there are the bigger companies such as Imecom, etc.
All of the images generated will be PDF or TIFF (likely). I don't know any that fax to an image.
As far as writing on the image, the prototype is Adobe, but Adobe is rather expensive. If you Google PDF software, you will find many third party programs such as CutePDF, NitroPDF and others. Some are free, many cost a small amount. Generally, the fancier you want to mark up, etc., the more it will cost. Almost all have trial periods.
