After searching for an idea to build my first online service, I discovered that one of the top 15 most searched tech-related queries in Japan is a safe PDF-to-QR conversion service.

So, I decided to build and self-host the service at home, offering a free 24-hour tier tailored to the Japanese market:

https://pdfqr.jp

Stack⌗

  • Frontend: HTML + CSS + JS
  • Network: Cloudflare + Docker
  • Backend: Go + Nginx + MariaDB + Purelymail

Goal⌗

Minimize friction for the user by reducing the number of clicks needed to get their QR code.

I also made it a point to collect as little personal data as possible to respect user privacy.

How does it work?⌗

The user visits the site, enters their email, selects how long the PDF should be available (24h for free, or a paid plan), uploads the PDF (drag & drop also works), and clicks to proceed.
If it’s a paid plan, a secure PayPal modal appears. Once the payment is complete, the PDF is uploaded and a database entry is created with an expiration date.

Data Privacy⌗

  • Email: Only used to send the QR code in case the user refreshes the page before downloading it.
  • Name and other details: Collected only by PayPal, in accordance with “Know Your Customer” regulations — never by me.
  • The database stores only the bare minimum needed to ensure service quality — for example, allowing refunds or deletion on request. The only customer-identifiable info stored is the email address provided by the user.

Data Deletion⌗

It’s simple: when the file expires (based on the chosen retention time), both the file and its database entry are completely deleted.
No soft deletion. No hidden tags. It’s gone.