I sometimes encrypt files, and delete the original (unencrypted) file using Eraser. Are there any remnants of the original unencrypted data remaining? I frequently use the "Erase Free Space" function, but I wasn't sure if this is enough.
If you use the Shadow Copies component of System Restore (and it is usually enabled by default), just erasing free space may well not be enough to remove all traces of deleted files. Erasing the target file directly (for example from the context menu) gives the best level of assurance. I find that disabling System Restore on non-system drives does usually make deleted files on such drives non-recoverable after a free space erase, so keeping sensitive files somewhere other than the C: drive may be a sensible part of a security strategy. There is, sadly, no one fix for computer security.