How to Use Watch Folders to Auto-Convert Files on Mac
To auto-convert files on a Mac, set up a watched folder: a Shortcuts or Automator Folder Action runs each time a file is added. Choose the folder, attach an action such as converting images or compressing PDFs, and test with a copy. Apps add safer defaults like not overwriting originals.
The built-in way
Folder Actions let a workflow run on files added to a folder. You build the workflow in Automator or Shortcuts. It is flexible but fiddly, and an error can fail silently.
Rules that keep it safe
Write results to a different folder or with a new name, never over the original. Ignore files that are still being copied. Test on copies. Keep a log you can read.
Paperlane for Mac recipes
Paperlane for Mac is a free native macOS app that automates file tasks on your Mac. Its recipes chain tools, run on a watched folder and write new files next to the originals. Files the app made itself are skipped, and half-downloaded files wait until they finish. Recipes use the same tools and limits as the window.
Limits
A watched folder needs the app or workflow to be running and the Mac awake. Test your workflow with copies before relying on it.
Frequently asked questions
Will Paperlane process its own output again?
Paperlane for Mac skips files it created itself, and waits for half-downloaded files to finish.
Can a watched folder run more than one operation?
Yes. Paperlane for Mac recipes can chain tools, such as rotating and compressing a PDF.