I don't know much about old documents, but you can try taking photographs with a range of different light colours, from infrared to ultra violet, both shining from the front (camera side) and from the back (through the document). Use RAW camera capture to enable PhotoShop manipulation. Try using a photo-scanner, front and back, set at the highest resolution possible, both photography and document settings.

Once good photographs are available fiddle with the best photography editor that you can find, such as PhotoShop. Include the use of black and white processing.