Does Sanity Studio auto-generate thumbnails for PDF files like images?

Sanity Studio doesn't automatically generate thumbnails for PDF files the way it does for images. This is a feature you'll need to implement yourself using a separate backend or service.

Here's what's happening and your options:

Out of the box:

• When you upload an image to Sanity, you get automatic thumbnail generation and the full Sanity Image API for transformations
• When you upload a PDF (or other file types) using the file field type, Sanity stores it as-is with metadata like filename, size, and MIME type, but doesn't generate preview thumbnails

Common approaches for PDF thumbnails:

1. Custom asset source plugin - Create a Studio plugin that intercepts PDF uploads, generates a thumbnail (first page as an image), and stores both the PDF and thumbnail. You'd typically use a service like:

   • A serverless function (could use Sanity Functions) to process the PDF with libraries like pdf-lib or pdf-poppler
   • Third-party services like Cloudinary or imgix that support PDF thumbnail generation

2. Post-processing with webhooks or Functions - Use Sanity Functions to listen for file upload events, generate thumbnails server-side, and store the thumbnail URL back in your document. Functions are the modern, recommended approach since they're serverless compute built directly into Sanity.

3. Client-side rendering - Use a browser-based PDF renderer like pdf.js to generate thumbnails on-demand in your frontend application

4. Hybrid approach - Store PDFs in Sanity but use a separate document type that includes both a file field (for the PDF) and an image field (for a manually uploaded or programmatically generated thumbnail)

The reason Sanity doesn't do this automatically is that PDF processing is computationally expensive and use cases vary widely (which page to preview, resolution needed, etc.). Most teams end up building custom solutions that fit their specific needs.