Compression runs in your browser instead of sending the document to a SonoFiles processing server.
Compress PDF Online
Reduce PDF file size with quality-first optimization or stronger visual compression modes, while keeping the original when compression is not genuinely beneficial.
Reduce your PDF file size
PDF • 200 MB recommended • up to 300 MB • one file at a time • no daily limit
Drop your PDF here
or choose a PDF from your device
The PDF is processed in this browser. SonoFiles does not upload it for compression.
PDF
Balanced compression creates a smaller visual copy. Pages are flattened to images, so searchable/selectable text, links, form fields, bookmarks and annotations may not remain interactive.
Required only for password-protected PDFs you are authorized to open.
Preparing…
Your compressed PDF is ready
Use quality-first optimization or three visual compression levels depending on how small the file needs to be.
Use the compressor again when you need it. The file-size limit exists for browser and device stability, not a paid unlock.
After compression, compare the original and output sizes plus the percentage reduction before downloading.
Compress PDF without guessing what the preset does
Reduce PDF file size for email, forms, application portals and storage. SonoFiles provides four modes so you can choose between preserving PDF structure and making a much smaller visual copy.
At a glance
- Recommended input: up to 200 MB for best reliability.
- Hard maximum: up to 300 MB per PDF.
- Page safety limit: up to 1,500 source pages.
- Large-file warning: files above 200 MB can need substantial memory; desktop is strongly recommended.
- Processing: local in your browser for this tool.
- No account, watermark or daily quota.
- Result: actual before/after size and percentage saved.
How to compress a PDF
1Choose a PDF
Select one PDF. Up to 200 MB is recommended; the hard maximum is 300 MB.
2Pick a mode
Choose Quality-first, Balanced, Smaller file or Maximum.
3Compress locally
Your browser processes the document on this device.
4Compare and download
Check the new size and save the result.
Choose the right compression mode
| Mode | Best for | Trade-off |
|---|---|---|
| Quality-first | Contracts, reports, digitally created PDFs | Preserves text/vector structure where possible; savings may be modest. |
| Balanced | Scans, mixed documents, email and everyday uploads | Good visual quality with stronger reduction; pages are flattened. |
| Smaller file | Application portals and stricter upload limits | Lower resolution and JPEG quality for a smaller result. |
| Maximum | Large scans where file size matters most | Strongest reduction; fine image detail can soften. |
Why compression results vary
A photo-heavy scan can shrink far more than an already optimized text PDF. File size depends on images, fonts, vectors, transparency, forms, annotations and how efficiently the source PDF was created.
SonoFiles does not promise a fixed percentage. The result panel reports the actual size before and after compression.
Preserve structure or make a visual copy?
- Quality-first: best when searchable text, selectable text and vector content matter.
- Balanced / Smaller / Maximum: render pages into compressed visual pages. This can reduce scans much more, but links, forms, bookmarks, layers and selectable text may be flattened.
Meeting email and portal size limits
Start with Balanced. If the result is still above the required limit, try Smaller file, then Maximum. No preset can guarantee an exact target such as 1 MB or 2 MB because every PDF is different.
Before submitting an important document, open the downloaded PDF and check small text, signatures, diagrams, QR codes and identification details.
Privacy and large-file processing
This compressor processes the selected PDF in your browser. Your file does not need to be uploaded to a SonoFiles compression server.
Large files: 200 MB is the recommended ceiling for best reliability, while the hard maximum is 300 MB and the source-page safety limit is 1,500 pages. Files above 200 MB are still accepted, but complex PDFs can consume much more working memory than their stored size; use a desktop browser when possible.
Tips for better results
- Start with Balanced for scans and image-heavy PDFs.
- Use Quality-first for text-heavy documents where structure matters.
- Check fine detail after Maximum compression.
- Keep the original as your archival copy.
- Avoid repeated recompression of the same visual PDF.
Choose Compression by Document Type, Not by the Biggest Percentage
A born-digital report, a scanned contract and an image-heavy presentation can have completely different reasons for being large. Quality-first compression is the safer starting point when text, vector graphics and existing image quality matter. Visual modes are better suited to scans when the destination has a strict byte limit. A large percentage saving is not automatically better if the output becomes difficult to read. The best result is the smallest file that still preserves what the recipient needs.
What Visual Compression Changes
Balanced, Smaller File and Maximum modes render pages and rebuild them with controlled image resolution and JPEG quality. That can strongly reduce scanned PDFs, but it also flattens page content. Native selectable text, vector graphics and interactive behaviour may no longer work exactly like the original. If Balanced already gets the document below a portal limit, there is usually no reason to use Maximum merely to chase a smaller number.
US, UK and European Portals Usually Publish a Maximum
Job applications, university submissions, insurance forms, government services and email systems often publish a maximum PDF size. Aim slightly below the ceiling because systems can calculate file size differently. If the portal also requires searchable text, a particular page size or specific document quality, satisfy those requirements before aggressive compression. A smaller PDF that no longer meets the document rules is not a useful result.
How to Inspect a Compressed PDF Properly
Check several page types in the output: the smallest text, a photograph, a chart and any signature or reference number. Compare them with the original at normal reading zoom and in print preview when printing matters. If the PDF contains digital signatures, forms or internal links, remember that rewriting or flattening can affect those features. Keep the source until the compressed version has been accepted.
Compress PDF frequently asked questions
Will compression reduce quality?
Quality-first avoids intentional visual downsampling. Visual modes trade more detail and page structure for smaller output.
Why did my PDF barely shrink?
The source may already be efficiently compressed.
Can I compress a 300 MB PDF?
300 MB is the hard maximum; 200 MB or less is recommended.
What happens to searchable text in visual modes?
Pages can be flattened into images, so native text behaviour may change.
Why can a digital signature stop validating?
Compression rewrites the signed document bytes.
Does SonoFiles keep a larger result?
No. A larger output is not treated as successful compression.
Useful Follow-Up Tools for a Compressed PDF
If size is now acceptable, no further processing is needed. Otherwise use the next tool only for document assembly or page separation.