To receive feedback about my novel from alpha readers, readers are emailed a private link to a PDF hosted on my website. Several readers have asked about submitting feedback by annotating the PDF in their browser.

I'm envisioning a pdf.js integration with pdf-lib leveraging a .htaccess interceptor. PHP on the back-end stores annotations in a .json file that corresponds to the PDF's filename. On each HTTP GET request to the PDF, a PHP script reads the corresponding JSON file and modifies the PDF on-the-fly with the annotations. When annotating, modifications are sent from the client using an HTTP PUT request, which is then appended to the corresponding JSON file.

Would this be useful to anyone else?

Does something like this already exist?