Ancient documents play an important role in history. Various information regarding the literature, tradition and culture is kept in these documents. These heaps of documents are degraded because of some climatic circumstances, low quality and inappropriate holding. This paper reviews on the techniques used to retrieve the necessary content from these ancient documents. The techniques include preprocessing, image binarization, thresholding methods and post processing methods. Further, during scanning the document it can get corrupted with some unwanted lines or signals termed as noise that should be eliminated.