Is there any useful documentation?
Is there any useful documents?
which is right or wrong? why?
Both are correct.
Document can be a piece of paper or set of papers with written or printed information, especially of an official type; such as an official document, a confidential or a legal document
Documentation may refer to the process of providing evidence such as a documentation for filing of a case in a court of law (usually termed as paper book) or to the communicable materials such as written and graphic that describe the use, operation, maintenance, or design of software or hardware.