Question 1

Are my PDFs uploaded to a server?

Accepted Answer

No. Thumbnail generation runs entirely in your browser using JavaScript. Your PDF never leaves your device, and the tool works offline.

Question 2

What extra features does this tool include?

Accepted Answer

5 thumbnail size presets (128/256/512/1024/original), 3 output formats (PNG/JPEG/WebP), page-range selection, custom background color, three bundle modes (individual files, ZIP archive, or single-image sprite sheet), sprite-grid calculator, page-orientation detector, thumbnail-quality scorer, multi-format metadata reports (text/CSV/JSON), and 20-entry history with shareable URLs.

Question 3

Does pdf-lib render PDF pages to images?

Accepted Answer

pdf-lib can read page dimensions, metadata, and structure but cannot rasterize page content to images. This tool generates dimension-accurate placeholder thumbnails (correct aspect ratio, page number, orientation indicator) and produces a complete metadata manifest (positions, sizes, filenames) that you can pair with a renderer like pdf.js or Ghostscript for the final raster. This keeps the tool 100% client-side with zero extra dependencies.

Question 4

What is a sprite sheet?

Accepted Answer

A sprite sheet is a single image that combines all thumbnails in a grid. It's smaller and faster to load than many individual files, and is commonly used for web galleries, document previews, and PDF viewers. This tool generates the sprite layout (grid dimensions, per-thumbnail x/y coordinates) and a metadata JSON so you can render it directly in your app.

Question 5

How does the page range work?

Accepted Answer

Use the same syntax as other UnQTools PDF tools: 'all', '1-3, 5, 8-10', '4-' (to end), or '-3' (from start). Invalid ranges are rejected with a clear error message.

PDF Thumbnail Generator

How to use