Lumen vs PDF24
PDF24 is a longstanding free PDF toolkit with a desktop app option. Lumen focuses on modern web-first UX, AI-assisted editing, and a signature/autofill vault.
Feature
Lumen
PDF24
Fully free everyday use
AI Assistant
Form autofill from saved profile
Signature library
Resume in-progress forms
Desktop app
Not needed — browser-based
24h share links
Modern UI
Watermarks
Never
Never
Ads
None
Yes on free
The bottom line
PDF24 is comprehensive but shows its age — cluttered UI and ads. Lumen is the modern pick if you value clean UX, AI assistance, and a workflow that remembers your form data.