This use of completed is right because it is not derived the verb request, but the substantive requirement. The suffix - ado adjectives form expressing the presence of the meaning by the primitive noun from which they are derived. Then, in the document completed sentence, this adjective points out that the document has the requirements to fulfil its role.
All fields of a registration form. Introduce or deliver the information requested to be able to run or issued something
Request does not appear in the dictionary of the Royal Spanish Academy. I know that in Mexico it is used, but that does not make it valid.
Action to fill the spaces in a format, which require data such as name, surname, street, Cologne, etc. The firm is part of the format requirements. At the conclusion of the action request format, the latter becomes record.