I assume you have a gradient in overall brightness due to unevben lighting. If that's the case, what you could do is to duplicate the layer with the image and apply the best correction to each part of the image on a different layer: curves for contrast, color balance or desaturate for white balancing.

Then, using layer masks you can paint each region with smooth gradients, in order to blend them together. Desaturation can be used as last step to even a bit the remaining differences.

An alternative approach could be to duplicate the layer (i took a picture with my hand shading half of the card, to reproduce the issue):

Blur it until the text disappears:

And then subtract the resulting layer from the original one select the blending mode as "Grain extract", in order to reverse the unevenness of the lighting:

The lowpass filtering that you achieve by blurring is only effective if changes in lighting are much smoother than the details of text, and it works best with sparser text as it disappears with blurring. Note that in this case, the bold text causes a halo when blurred, which gets inverted when doing the blending. You can try with a larger radius, or try masking it before blurring the duplicate layer.

Also, note that this operation also fixes the white balance as it inverts the color curves.

As a final touch I applied the 'Curves' setting to increase contrast.

It may not be perfect but I'm actually surprised by how that one came out.