I have photographed pages from a book beyond copyright but the copystand light has caught the curved page and lightened the text there on left edge of page, then in the middle its got the right balance of black text to light grey background, then as the curve bends right the page background colour has gone a bit darker though the other right hand lamp has avoided too much of that, as such opening it in photoshop and adjusting levels to remove the hill at right in the histogram to whiten up the page background, and dragging the black slider in to sort out the grey text, is giving an overall attack when I need to be able to paint a levels effect if you see what I mean, set a tool to different levels settings to suit different parts of the page.
I try for burn but the light grey background as well as the text goes dark, I just want to darken the text and not the background on the area that caught the light more. I need to have the effect get less as I work my way across the page, so the idea of painting a correction seems ideal., especially as the lighter area is not evenly down the page edge but more in the upper portion nearer the copy stand lamp.
I have many pages to do like this, there was no way of flattening the book.
Without seeing the page, it's hard to tell, but I might try using the gradient tool, and adjust the contrast and exposure as best you can, and if you can't get both to your liking, try adding another gradient adjustment just targeted at either the type or background that you couldn't get proper exposure, then use the range mask to include just the areas you want to target.
In the future, I would make a custom book holder that holds the left and right sides at 90 degree angle, so the pages lay flat. I would also use cross polarizing filters to revolve any glare.