Yes, there are hundreds of extant written contracts describing this particular function. They are commonly called charters (Lat. cartas) and while the oral and ritual aspects were always a part of these specific tenurial agreements (the statement of intention, volo, and the oath of fidelity, which might specify the terms of the contract) charters were an increasingly important tool from the eleventh-century onwards (although they had always existed it simply wasn't as common to consistently record contracts in this manner) and by the end of the Middle Ages it would be almost unthinkable for a lord not to keep track of his major tenurial dues through written record.

Of course, we do not have the original in every case. They might have been copied onto rolls or in a cartulary, such as that of the Trencavel family. This wiki page describes the cartulary and also contains an excellent set of studies on the topic (esp. Kosto's Making Agreements in Medieval Catalonia). To this I would add the definitive study of English documentary culture, M.T. Clanchy's From Memory to Written Record in England, 1066-1337, 3rd ed., (London, 2013).