ProperPDF is made by one independent developer. It started from a simple annoyance: most phone PDF tools want you to upload a document, make an account, or watch an ad before they'll merge two files. ProperPDF does the everyday PDF jobs on the phone instead, with no account, no ads and no uploads.
How it's built
There are two native apps rather than one shared codebase. The iPhone and iPad app is written in Swift with Apple's PDFKit. The Android app is written in Kotlin with Jetpack Compose and the PDFBox library. They share a design and a feature list, so a tool works the same way on both.
How it makes money
Pro unlocks compress, sign, fill forms and password protection, and removes the watermark from free exports. That's the only income: no ads, and no selling of data. You can pay once for lifetime access instead of subscribing.
Contact
Bug reports, feature requests and questions go to hello@tryproperpdf.app, and a person reads every one.