Help removing shadow edges on text documents

Can you automate this process or would I have to do this page by page?

This is uneven lighting, and that's what you need to correct. You need an adjustment layer with a layer mask.

Make a Curves or Levels layer that pulls the darkest part (upper left corner) up to full white. Then add a layer mask, press ctrl+I to invert the mask. The mask should now be fully black to hide the adjustment.

Then use a soft brush to paint the adjustment in gradually, bringing the shadowed portions up to full white.

The mask will look something like this:

And the final result:

Add a Levels adjustment layer. Drag the right [highlight] slider to the left, to clean up the shadows, and then drag the center [gamma] slider slightly to the right, to put some oomph back into the blacks. Don't drag it too far, or the detail in the black line art will start to block up.

Try different tolerances of the magic eraser.   You can also try adjusting the brightness and contrast in combination with that.