To put it into its simplest form:
The requirements documentation is one or more documents where you write down all the requirements for your project.
The requirements traceability matrix on the other hand is a table (or spreadsheet or some feature of your PM software) that takes all the requirements and maps them to the deliverables to ensure that each requirement that you have is actually satisfied.
See PMBOK Guide Glossary: 6th edition page 719 or 7th Edition page 247