How to Compress a PDF (Without Losing Quality Where It Matters)
Why PDFs get big, the difference between lossless and strong compression, and how to get under email and portal upload limits.
Editorial disclosure: Pyalm publishes and maintains the products and free tools discussed on this site. Regulatory statements are linked to primary sources where applicable. No independent professional review is claimed unless a reviewer is explicitly named.
Email attachments cap out around 20–25 MB, WhatsApp documents at 2 GB but portals often at 1–5 MB. A scanned contract or image-heavy brochure blows past those limits easily. Here's how to shrink a PDF intelligently.
Why PDFs get large
- Scanned pages are full-page images, often at 300–600 DPI.
- Photos embedded at camera resolution.
- Embedded fonts and duplicated resources from repeated exports.
- Unused objects left behind by editing.
Two kinds of compression
| Lossless | Strong (re-render) | |
|---|---|---|
| How | Rebuilds file structure, packs objects into streams | Renders each page to an optimised JPEG |
| Text stays selectable | ✓ | ✗ (pages become images) |
| Typical saving | 0–30% | 50–90% on scans |
| Best for | PDFs exported from Word, Excel, accounting software | Scans, photo-heavy documents |
How to compress a PDF
- Open the free Compress PDF tool.
- Start with Lossless. If the file is still too big, switch to Strong.
- In strong mode, adjust resolution and JPEG quality — 110–150 DPI at around 70% is sharp on screen and small.
- Check the before/after size, then download.
Hitting a specific size limit
Portals often ask for "under 1 MB" or "under 2 MB":
- Lower DPI first (120 → 96), then quality (70% → 55%).
- Tick greyscale for black-and-white documents — it often halves the size again.
- Split very long documents with Split PDF and upload in parts if allowed.
Keep your original
Strong compression turns text into pictures, so the result can't be searched or edited. Always keep the original for your records and send the compressed copy.
Avoid big PDFs in the first place
Scan at 200 DPI rather than 600 for documents, export from Word with "Minimum size" when it'll only be read on screen, and resize photos before inserting them — the Image Compressor helps.
Why browser-based PDF tools are safer
Most online PDF sites upload your file to their servers. Pyalm's PDF tools run entirely in your browser — the file is read, processed and saved on your own device and never sent anywhere. That matters for contracts, invoices, bank statements and ID documents.
Stop handling business PDFs by hand
Most business PDFs are invoices, quotations, receipts and statements. Pyalm Books generates them for you — VAT-compliant, numbered, emailed to the customer and stored — so there's nothing to merge, rename or fix afterwards.
Related free tools
Merge PDF | Split PDF | Compress PDF | PDF Editor | Sign PDF | All free tools