A metal file smooths rough edges by wearing them down, so it is read as refinement and patience. Dream books link it to polishing a plan or softening a sharp manner.
When this appeared in your dream, what were you feeling?
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.