Why didn't my PDF get smaller?

Some PDFs are already tightly packed. If the file was produced by a professional tool (Adobe Acrobat, Affinity Publisher) with optimization enabled, there may be little left to remove. PDFs with many large embedded images are the hardest to compress without re-encoding those images.

Can I compress a scanned PDF?

Yes, but expect modest results. Scanned PDFs are essentially image containers — each page is a rasterized bitmap. Structural compression helps a little, but the images themselves are the bulk of the file. To significantly reduce a scanned PDF, you'd need to re-encode the page images at lower quality, which this tool deliberately avoids to preserve readability.

How does this compare to Adobe Acrobat's compression?

Adobe Acrobat's 'Optimize PDF' feature does more — it can downsample images, remove embedded fonts, strip metadata, and flatten form fields. This tool applies structural compression only: object stream packing and cross-reference optimization. It's lossless, but less aggressive than Acrobat's full optimizer.

Is there a file size limit?

No hard limit is imposed by the tool. The practical ceiling is your device's available RAM — most modern computers handle PDFs up to several hundred megabytes without trouble. Very large files (500 MB+) may slow down on older hardware.

Can I compress multiple PDFs at once?

Yes. Drop several PDF files onto the tool and each is compressed independently. Results are shown per file so you can see the savings on each one before downloading.

What's the maximum number of pages I can compress?

There is no page limit. The tool processes the full document structure regardless of page count. A 500-page annual report compresses the same way as a 2-page invoice.

Will the compressed PDF open in all PDF readers?

Yes. Object stream compression (PDF 1.5+) is supported by every major reader: Adobe Acrobat, Chrome, Safari, Firefox, Preview on macOS, and all modern mobile viewers. Very old readers (Acrobat 4 and earlier from the early 2000s) don't support it, but those are effectively obsolete.

Can I compress a password-protected PDF?

No. Encrypted PDFs cannot be read or restructured by pdf-lib in the browser. Remove the password protection first using a tool like Adobe Acrobat, then compress here.

Is my PDF uploaded anywhere?

No. Everything runs in your browser using JavaScript. Your files never leave your device — not even temporarily. There is no server involved.

Is it safe to compress confidential documents here?

Yes. Because compression runs entirely in your browser with no server communication, confidential documents — contracts, financial statements, medical records — are safe to process here.

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When you need to compress a PDF

PDFs accumulate bloat over time — every edit, re-save, and annotation pass can leave behind redundant objects and unoptimized structures. The result is files that are larger than they need to be, which causes real friction.

→Email attachments rejected because the file exceeds the 10–25 MB limit
→Document portals (legal, medical, HR) that cap uploads at a fixed file size
→Sharing via messaging apps that compress files or reject large attachments
→Slow load times when embedding a PDF in a website or web app
→Storage limits on cloud drives or archiving systems
→Slow rendering on mobile devices with limited memory
→Reducing the size of merged PDFs before sending to a client
→Compressing a report before attaching it to a submission form

How PDF compression works

PDF files are made up of objects — pages, fonts, images, streams, and metadata. When a PDF is created or edited repeatedly, it can accumulate redundant cross-reference entries, duplicate objects, and unoptimized stream data. This tool re-packs the file using object stream compression, which groups multiple objects into a single compressed stream.

The result is a smaller file with identical content. Unlike tools that downsample images to reduce size, this approach preserves every pixel and every character.

What compression can and cannot do

Structural compression targets the PDF container — the overhead, not the content. This means it works best on PDFs with many redundant internal objects: repeatedly edited documents, forms, merge results, or files exported from tools that don't optimize output. The savings can be substantial — 20–50% on bloated files.

What it cannot do: reduce the size of large embedded images. If a PDF is mostly high-resolution photos or scanned pages, those images are the dominant size factor. Structural compression won't touch them. In that case, re-exporting from the source application at a lower image quality, or using a tool like Adobe Acrobat's image downsampler, is the right approach.

How to compress a PDF

1
Drop your PDF
Drag a PDF onto the compressor or click to browse. You can compress multiple files at once.
2
Wait for compression
The compression runs in your browser using JavaScript — no upload required.
3
Download the compressed file
Click Download next to each file to save the compressed version. The size reduction is shown next to the filename.

Compress then merge — or merge then compress?

Both orders work, but merging first is usually more efficient. When you merge PDFs, the resulting file may contain duplicate fonts and shared resources that can be deduplicated in a single compression pass. Compressing each file individually before merging misses that opportunity. For the best size reduction: merge first, then compress the combined file.

Related tools

Merge PDF — combine multiple PDFs, then compress the result
Split PDF — extract individual pages into separate files

Frequently asked questions

About Compression

It depends on what's in the PDF. Files with a lot of redundant structure (many small objects, unoptimized cross-reference tables) can shrink significantly. PDFs that are already well-optimized may see minimal reduction. The tool shows you the exact savings after compression.

No. This tool reorganizes the PDF's internal structure and deduplicates objects — it does not re-encode images or alter content. Text, images, and formatting remain identical.

File Size & Limits

Compatibility

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