investigation about usage of “document” in sense of formal written in persian texts

the term “sānād” i-e (persian historical document) is an important key word in history. although there are many researches about purport, applicable field of “sanad” but historical linguistic of this term is little-known. in regard to that this word have not a long use by mean “written” and “document” in  iranian historical texts, therefore  mind question of this article is: when this term in recent mean, used in  islamic historical text? results of this article prove that “sanad” by different sense and late 15th century, has become common through persian texts, particularly administration texts.