Ultra-Fast Android Billing App

I need a lightweight Android invoicing app that can push out ten to twelve invoices in roughly two minutes. Speed and simplicity come first. On the entry screen I only want to choose items and their quantities, nothing more. When I tap “Save,” the app should immediately create a clean PDF, store it on the device, and open Android’s native print dialog so I can send it straight to the printer—no emails, no messaging.

Performance targets: the full path from launching the app to holding a printed invoice should stay well under twelve seconds per customer on a mid-range phone. Everything must work offline; a small local product list that I can update quickly is fine, but I do not want sign-ups or cloud syncing.

Deliverables
• Signed APK ready for installation and the full, well-commented source code
• Simple guide for adding or editing products, unit prices, company logo, and header details
• List of any third-party libraries used with their licences

Acceptance criteria: during testing I must be able to generate and print twelve separate PDF invoices within two minutes, with no formatting or print errors.