A file or folder is read as a piece of memory or knowledge put away for later. Losing one in a dream stands for something forgotten; opening one for a past matter brought back to light.
Where in your waking life have you met something like this lately?
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.