For a very thorough introduction to primary sources with an archival focus, see the Primary Sources research guide, as well as the "Using Archives and Manuscripts" section of this guide. Note that in the field of book history, a book (or periodical publication, or online source) can be both a primary and a secondary source, depending on your research focus.
17th & 18th Century Burney Collection Newspapers contains the digitized materials (not just newspapers) collected by the Reverend Charles Burney (1757-1817) and held in the British Library. A useful source for find information about the United Kingdom and the wider world in the seventeenth and eighteenth centuries.The database's advanced search offers searching publications by title, place, language, section, and date. The Publications Search link includes searching by format, including (among others) books, broadsides, forms, newspapers, and pamphlets.