While writing a novel, I’d like to get feedback from alpha and beta readers. Currently, I build a PDF and send an email to each reader individually. A number of readers have requested the ability to send me feedback by adding annotations to the PDF directly. Ideally, without having to install any software on their laptop, desktop, or phone.

Do you know of a super-simple drop-in server-side PHP solution that allows users to edit PDF files and persist changes? Simplicity is key here:

• integrates with an existing web server (nginx or apache);
• uses PHP for handling server-side requests;
• has a zero authentication mode (links are always private);
• does not use cloud or SaaS;
• integrates with .htaccess files; and
• uses a flat file system (no SQL database).

Here’s how I imagine it’d work:

1. Author creates a PDF.
2. Author publishes a PDF to web server.
3. Author sends PDF link to a Reader.
4. Reader clicks PDF link.
5. Magic:
   1. Web server intercepts PDF link and redirects to PDF editor (e.g., pdf-lib).
   2. Web server pre-loads existing annotations from file and adds them to PDF.
   3. Reader’s browser receives PDF, with any existing annotations added.
6. Reader annotates PDF.
7. Web browser sends annotations to server.
8. Server persists annotations in file.
9. Author clicks PDF link, which shows all annotations made so far (by magic).

If there isn’t such an open-source tool, would anybody be interested if I were to build such a system?