PDFvcon is a GUI front-end for Ghostscript that converts the version of a PDF document. If you have software that can accept only up to version 1.4 of a PDF document and the file you have is 1.6, then this is your answer. It was created out of a need for the author to be able use some of his old Windows software.
GTK+ Recent Files Scrubber is a compact, lightweight Python script which uses GTK's RecentManager to watch for updates to all globally-available "Recently Used" lists (the ones which appear in Open dialogs and the like) and filter out anything in the folders you blacklist. Blacklist entries are hashed to make reading the blacklist not worth the effort.