1. A document reading device comprising: a document image acquisition unit that reads a document and obtains a document image; a memory that holds the document image obtained by the document image acquisition unit; a determination unit that determines whether or not a size or orientation of the document, the image of which is obtained by the document image acquisition unit, matches a set parameter; and a setting change unit that, when it is determined that the size or orientation of the document does not match the set parameter, changes a setting of the parameter so as to match the size or orientation of the document.