Example implementations relate to detecting document objects. For example, detecting document objects may include a system comprising a pre-processing engine to establish a threshold for a document, wherein a structure of the document is unknown, a detection engine to detect a candidate area in the document, using a Hough transform and connected component analysis to merge detected candidate areas in the Hough transform to a same document object in the document, and a classification module to classify the candidate area as a document object or not a document object.