Compress a PDF without wrecking quality

A 40 MB scan will bounce from email and corporate portals. Compression fixes that — unless the tool re-encodes everything into a blurry image soup or forces an upload. You can compress PDFs privately in the browser and choose how aggressive the tradeoff should be.

What actually makes PDFs large

• High-DPI phone or scanner images embedded at full resolution
• Unoptimized JPEGs or lossless images that never needed print quality
• Duplicate fonts and leftover objects from export pipelines
• Multiple merges of already-heavy files without an intermediate shrink

Text-heavy reports exported from Word are often modest. Photo-heavy decks and multi-page color scans are where size explodes — and where smart image re-encoding helps most.

Pick the right compression level

Light

Best first try for documents you still need to edit or archive with selectable text. It targets oversized images without turning every page into a flat picture.

Recommended

Balanced default for email and web upload forms. Text usually stays selectable; images are re-encoded more firmly. Use this when Light barely moved the needle.

Extreme

Smallest size for rough previews or secondary copies. Pages may be rasterized, so text can stop being selectable. Prefer Extreme only when a portal’s hard limit leaves no alternative — and keep the original elsewhere.

A practical workflow that protects quality

1. Keep the original PDF untouched on disk.
2. Run Light compression and compare sizes in the tool.
3. If still too large, try Recommended and spot-check a text page and a photo page.
4. Only then try Extreme, or crop/remove unused pages first with Organize Pages.
5. If compression cannot help, StackPDF returns the original with an “already optimized” style outcome instead of shipping a bigger file.

Compress before or after merge?

If every source is already heavy, compress each scan first, then merge — you avoid one giant intermediate file. If sources are mixed (a small text PDF plus one huge scan), merge first only when order matters more; otherwise compress the scan alone, then merge. After a large merge, a final Recommended pass is often enough for email.

Privacy note

Cloud compressors see every page of tax packets and IDs. StackPDF’s compressor never uploads the document for processing. That is the right default for personal archives and workplace docs with retention rules.