Dear Student,
Through the medieval period paper gradually became cheaper and morewidely available.
And manuscripts means written by hand so people used to write holy texts, chronicles of rulers, letters and teachings of saints, petitions and judicial records, and for registers of accounts and taxes. So Manuscripts become an important source for information in middle ages,
Also Manuscripts were collected by wealthy people, rulers, monasteries and temples. They were placed in libraries and archives. And these manuscripts and documents provide a lot of detailed information to historians.
Regards