I built a Letterhead Editor—a fully air-gapped, offline-first Android and PC webapp designed to help professionals or organizations draft letters in a standard format.
It allows the user to input dynamic credentials, digital signatures, and local QR codes, outputting a perfect vector-based PDF. I completely stripped all INTERNET permissions from the Android Manifest to ensure it is 100% tamper-proof and offline.
The hardest part by far was fighting the Android WebView engine and its native Print Spooler. Porting a desktop-first CSS layout to mobile trapped me in a non-scrollable “100vh prison” at first. Then, getting the Android PDF generator to strictly respect A4 dimensions without adding ugly black margins or randomly splitting into two pages took hours of media-query debugging. I even had a 0.5pt “security micro-text” feature that worked flawlessly on PC, but I eventually had to write a kill-switch to axe it from the mobile build because Android’s accessibility auto-scaler aggressively refused to let text render that small!
I figured it out by hard-locking the print dimensions to 296mm to satisfy the print spooler, moving my QR library from a CDN to a local asset, and using a Java JavascriptInterface bridge to handle native printing securely. I am really proud of the fact that it is completely “ghost” software—it operates completely offline with zero data leaks.