Improving document copy

What machine are you using to do it?  Normally on a scanner or all-in-one, you can select a higher resolution to include more detail.  You can also select the relative density on some and give more weight to the dark or light.  Grayscale works better than color for some documents.

What type of paper is used for the originals? Is it like old thermal fax paper or normal photocopier-type paper?

Thermal paper solution:

If it is thermal paper, you need to be careful. Try this first on something that you don't mind losing (in case it does not work or ruins the test paper:

Put your iron, yes your wife's iron, on the "Wool" heat setting and  cut off the  steam, if any. Place your fax face down on the ironing table and rapidly iron your fax. Wait a couple of seconds and then go and photocopy it or scan it, Or you could scan the resulting photocpy.

How it works or what happens : evrywhere where there is nothing written becomes black and what was drawn or written becomes white.

Regular paper solution:

For regular paper, you would probably need to use photocopy it first, using photocopier darkness settings to improve the darkness. Then you could scan the resulting photocpy.

I have some old military document from when I was in the Army. Some of the document has important info that is almost to light to read. Since you can restore pictures why can't you restore documents?

Solution is really about what I thought but no one came up with anything better.