Yes. What you’re trying to fix is perspective distortion (also called keystone distortion). Many image-editing programs can correct it by letting you adjust the document’s corners until the page becomes rectangular again. One free desktop option mentioned is GIMP, which includes a perspective tool for this kind of correction. In general, look for features named perspective correction, keystone correction, or transform. For the cleanest results, photograph the document as square-on as possible with even lighting, then apply the perspective adjustment afterward.