Documentary Sources:

Those  information which are contained  in  the published and unpublished documents, reports, statistics, manuscripts, letters, diaries  and so on, are grouped under  two  broad categories,  i.e, primary sources and secondary, sources. 

• Primary sources provide data which are gathered at first hand where the responsibility and promulgation remain under the same authority that originally gathered them. Data from primary sources may  be  gathered by observation, personal interview, conference, correspondence, questionnaire and  other devices, 
• Secondary sources provide data that have  been  transcribed or compiled from original sources; here the promulgating authority is different from the one which  controlled the collection of data at first hand,  e.g.  the Census of US  is generally cited as the primary source whereas the Health Statistics on  India based on Census of India are examples of the Secondary Source. Note that promulgation means publication, dissemination, making known  to public  or exposing to public.