NotePen

A Kotlin Multiplatform PDF and document annotation app with an infinite canvas, tuned for stylus input.

Features Infinite canvas. Annotate on an unbounded surface that extends past the page, so notes, sketches, and mind maps are not constrained by the document margins. Natural ink over PDF. Import a PDF and draw or write over it like digital paper, with pen-pressure support tuned for stylus input. Graphics tablet and stylus. Pen input with pressure and tilt, the barrel (side) button, and the eraser tip. Windows uses WinTab (Wacom and compatible tablets), macOS uses Cocoa tablet events, and Android uses the built-in stylus. Marker / highlighter. A dedicated marker tool for highlighting content over the document. Eraser. Remove strokes. Erase operations are modeled as tombstone deltas, so they also propagate through sync. Smart shape gestures. Draw freehand, then hold the pen or finger to snap a sketch into a clean straight line or a selection, using on-device shape recognition and simplification. Handwritten links. Circle a piece of text or draw a symbol to create an interactive link to another page of the same document or to an external resource. Reflow reading mode. Extracts and re-flows document text into a comfortable reading view, with reading-comfort presets (built-in and custom), while keeping your annotations anchored to the text. Multi-page viewer. Read page by page in a single-page layout or a two-page spread, with a magnifier for precise stylus placement. Autosave. Edits are saved as you go. Close a document and come back later with annotations intact. Peer-to-peer LAN sync. Sync annotations between devices over the local network using Ktor WebSockets and mDNS discovery, with last-writer-wins merge per document. No cloud involved. QR-code pairing. Pair devices by generating and scanning a NotePen QR code. EPUB / FB2 conversion. Built-in conversion turns EPUB and FB2 e-books into paginated documents you can annotate like PDFs.