Hypothesis annotation on mobile device is possible via browser extension (on kiwi & firefox, for example) and via.hypothes.is. However, the former doesn't support pdf; the latter requires to host the pdf on certain server in advance, which is tedious and sometime impractical.
This web app modify hypothesis/pdf.js-hypothes.is and enable user to view and annotate pdf directly on mobile device, or any device without extension installed.
Please enter here and follow the instruction to annotate your pdf file.
No file is uploaded to remote server while opening.
The annotation you made can't be visited by url from User Page, so you'd better name your pdf's title metadata properly for convenience.
Make it a PWA (Currently tabbed PWA isn't official yet, may need a large remake of whole framework)