When one of our clients prepared to migrate from WooCommerce to Shopify, there were a number of features that had to be re-created, one of which was PDF upload: allowing customers to upload large-format sewing pattern PDFs and automatically calculating the correct price based on page count and size.  On their old site, this workflow was custom-built, we needed to reproduce it cost-effectively and reliably on Shopify.

The problem

Rebuild the existing PDF-printing workflow with clear requirements:

• Customers upload a PDF to purchase a printed version
• Pricing must adjust based on page count
• The uploaded PDF should be verified to:
  • Ensure it is the correct size (must be A0, A1, or A2)
  • Confirm the number of pages
• The uploaded file must be accessible in:
  • Shopify Admin
  • My Account
  • Order confirmation email

Our approach

We set constraints from the outset:

1. Use Shopify’s standard functionality wherever possible
2. Only use apps that closely fit the requirement (and have a 4.5★+ rating)
3. Minimise development complexity
4. Keep ongoing maintenance low

The goal was a robust, scalable solution without unnecessary customisation.

The solution

1. File handling via Upload Kit
After reviewing options, we selected Upload Kit to manage file uploads. It provided:

• PDF upload before add-to-cart
• File visibility in the basket
• File access in Shopify Admin
• File access in My Account

This covered the majority of the brief without custom development.

2. A micro-service for PDF validation and pricing
To address the remaining logic, we built a lightweight micro-service that:

• Validates the uploaded PDF size (A0/A1/A2)
• Blocks the purchase if the file is not a supported format
• Counts the number of pages
• Automatically selects the correct product variant based on page count

This ensured accurate pricing and prevented invalid orders before checkout.

Outcome

The final solution is simple, reliable and easy to maintain. It reproduces the original workflow while taking advantage of Shopify’s ecosystem, and it has performed consistently from day one

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