A display processing apparatus includes a first acquisition unit for acquiring light source information including a first relative position of a light source with respect to a display unit, a detection unit for detecting posture information of the display unit, a second acquisition unit for acquiring the posture information, a third acquisition unit for acquiring document data, a calculation unit for calculating a second relative position of the light source with respect to the display unit, a generation unit for generating a document display surface where a state in which a document surface displaying the document data is disposed in a virtual three-dimensional space and also the light source is disposed at the second relative position with respect to the document surface is converted to a two-dimensional image, and a display control unit for executing control to display a preview image on the display unit.