You open the PDF and watch the spinner. Five seconds. Ten. Finally a page appears. You scroll, and the next page redraws while you wait.
This is what 80MB of uncompressed scans feels like to a viewer. The fix is straightforward.
What's actually going wrong
Three things make PDFs slow. Big files. Anything over 50MB is going to feel sluggish on most machines. Unoptimised structure. The PDF wasn't 'linearised' — viewers can't show page one until they've read the whole file. Heavy graphics. Per-page transparency, layered objects, and embedded vector art make rendering slow even for small files.
File size is the most common culprit. Compression usually solves it in one step.
The quick fix
Drop the file into compress PDF. Flint's compressor downsamples images, optimises structure, and linearises the output. Most slow PDFs come back smaller and instant-to-open.
If the file is mostly text and the slowness is structural, compression will linearise even without major size reduction, and pages will start appearing while the file is still loading.
If that didn't work
Test the file in a different viewer. Some viewers are slow regardless of file quality. Chrome and Edge are fast; older versions of Acrobat can be painful.
If the file has heavy graphics that compression can't help with, convert to JPG (which rasterises each page) then convert back to PDF. You lose searchable text, but loading becomes instant.
For scanned documents, OCR via convert PDF to Word and re-export typically produces a faster file because the structure is rebuilt clean.
Prevent it next time
Compress PDFs before storing or sharing. Don't open large PDFs straight from cloud — download first. Keep your viewer updated. And avoid embedding huge raw images in source documents — resize them first.
FAQ
What's a 'linearised' PDF?
A PDF structured so viewers can display page one immediately while the rest of the file streams in. Non-linearised PDFs make the viewer wait for the whole file before showing anything.
Does compressing affect quality?
Flint compresses images to screen resolution which is invisible during normal reading. Text stays vector-sharp. For typical office documents the visual change is undetectable.
Why does my PDF open slowly only over wifi?
Streaming a large non-linearised PDF over a slow connection waits for the entire file. Either download first, then open, or linearise the file via Flint's compressor.
Why do scanned PDFs open so slowly?
Each scanned page is a full-resolution image. A 30-page scan can be 100MB+ uncompressed. Compression typically shrinks scans by 90% with no visible quality loss.
Don't accept slow PDFs. Compress in Flint once and the file opens instantly for every viewer, every device, forever.