PDF compression is mostly about image re-encoding. Text in a PDF is stored as vector glyphs or embedded fonts and compresses almost perfectly with no quality loss. Images — scans, photos, charts, logos — are the bulk of the file size, and they re-encode at lower quality to shrink the file.
The trick is knowing which quality level to pick for the situation.
The four presets, in plain English
Most PDF tools offer four quality levels. Here's what each actually does:
- Screen (72 DPI) — smallest files, lowest quality. Fine for a quick preview but text starts to look fuzzy. Good for: sharing a draft, attaching to a chat message.
- eBook (150 DPI) — the sweet spot. Cuts file size by about 60% on a typical scan while keeping every word legible. Good for: emailing a receipt or contract, attaching to a form upload.
- Printer (300 DPI) — preserves the original quality. Files shrink modestly (10-30%) because most of the bloat is already optimized. Good for: documents that will be printed or reviewed closely.
- Prepress (300 DPI, no downsampling) — identical quality to the original, files don't shrink much. Good for: sending to a print shop.
For most business uses, eBook is the right answer. The text stays sharp because text isn't re-encoded — only the images are. The result reads identically to the original on screen.
How to do it in DocShop
- Open the Compress PDF tool.
- Upload the file. eBook is the default — leave it for typical business documents.
- Click Make it smaller.
- Compare the result. The page count and dimensions don't change. Only the file size shrinks.
If the result isn't small enough, run it through a second time — each pass shrinks further, though quality loss does compound across passes (a second pass on an eBook PDF will start to show some softening around text edges). Or drop to Screen preset if you only need it for screen reading.
When compression can't help
A PDF that's already at eBook quality won't shrink much further — most of the bulk is already optimized. Same for PDFs that are mostly text with few scans. Stop here and upload the file as-is.
For image-heavy files (a 200-page scan of a book), the right tool is often PDF to JPG — extract just the pages you need as images, at lower DPI, and attach those instead of the full PDF. Useful for sharing a single page from a long document.
Don't compress documents you'll sign
If a contract is going through DocuSign or a similar e-signature platform, don't pre-compress it. The signature service re-encodes the file anyway, and pre-compressing can interfere with the signature layer. Send the original PDF to the signature platform and let them handle the encoding.