How can I restore my old books?

I suppose you can take a photo of every page and then use OCR software to convert it to a word document? I guess it depends on what your goals are. Do you want to reprint your book?

I think the first thing you should do is scan your entire book if you don't want to lose it. If some scans are hard to see, then you can programmatically enhance image. After all the scans are ready, you can find a professional who will bind you a new book on new paper from these materials that you have prepared. It is easier and cheaper than restoring an old book.

There are professionals who can restore books, sometimes.
They work for museums and rare book collectors.
They are expensive...
They'd leave you with a book that's hopefully in a better state or at least no worse and longer lasting, but at a (rather steep) price.

If you want to just recover the data, either try using a scanner and OCR software as suggested or type out the content of the book as you are reading it.

Try to scan them on the phone or scanner, and then print it. I think it's may help :)

Just take photos of the pages and rewrite it manually or by any software like Optical Character Recognition.