1. An electronic document comparison system, comprising: a storage system; a database system that stores a standard electronic document; at least one processor; and an electronic document comparison unit stored in the storage system and being executable by the at least one processor, the electronic document comparison unit comprising: a preprocessing module operable to preprocess a test electronic document to remove cachets and noise from the test electronic document; an identifying module operable to identify the test electronic document using optical character recognition (OCR), and generate a plurality of second minimum blocks and obtain coordinates of each of the second minimum blocks; a comparison module operable to compare each of the second minimum blocks with a corresponding first minimum block in the standard electronic document line by line, and obtain the second minimum blocks having different coordinates on each line; a filtration module operable to simplify the obtained second minimum blocks having different coordinates by filtering designated objects; and a mark module operable to mark the simplified second minimum blocks in the test electronic document.