This demo needs to be served over http://
You have opened it from the filesystem. Browsers refuse to load ES modules or fetch files
from file://, so the engine cannot start. Serve the folder and open the address it prints:
cd site && python3 -m http.server 8000
# then open http://localhost:8000/demo/Starting the engine…
This is the SDK’s own PdfViewerElement, mounted in four lines with
the toolbar it ships. Pick a tool and draw on the page — the stroke or region follows your
pointer as you drag. The note tool asks for its text; redaction removes the content rather
than covering it. Save downloads the edited file.