A certificate is read as proof — something earned and officially confirmed. In dreams it can stand for the need to have your worth or skill validated, or the relief of a stage completed.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.