On-device processing

For documents, on-device processing means the file is opened, changed and saved inside the app, with nothing uploaded. It keeps working without a connection and leaves no copy on a server.

The main alternative is server-side processing, where the file is uploaded, changed on a server and sent back. That can suit batch jobs, but every document then passes through a system someone has to run, secure and pay for, and the app stops working when the network does.

On the device, the privacy case is simple: a file that is never sent can’t be intercepted on the way or leaked from a server. That can make reviews easier for apps that handle medical, legal or financial documents, though it doesn’t replace your own compliance work, because the app still has to store files responsibly.

There are limits. The work uses the device’s memory and processor, so very large files depend on the hardware, and an update reaches users when they update the app. For most interactive editing those limits matter less than getting an instant response and working offline.

It is also a question of cost and speed. There is no document server to scale as usage grows, because each user’s device does its own work, and nothing has to travel over the network before the user sees a result. A busy day for your app doesn’t become a busy day for your servers.