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Compress PDF

Re-save a PDF with object-stream compression. Text-heavy files get smaller and nothing on the page changes.

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smaller{ stream }Object streams (PDF 1.5)

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Quick answer

This tool shrinks a PDF by re-saving it with object streams, a PDF 1.5 feature that packs the document's many small objects into compressed blocks. It is lossless, so the file looks exactly the same, and it runs in your browser with pdf-lib. Expect roughly 10-25% off a text- or vector-heavy file. It does not downsample images, so scans and photo-heavy PDFs may barely shrink, and the tool tells you when that happens.

  • ~10–25%typical saving on text PDFs
  • Losslessno image downsampling
  • PDF 1.5object streams
  • 0files uploaded

What the Compress PDF does

A PDF is made of thousands of small objects: text runs, font data, page descriptions and metadata. In an inefficiently saved file each object carries its own overhead. This tool rebuilds the file with object streams, which gather many objects into compressed blocks, so the same document takes fewer bytes.

The compression is lossless. No pixels are thrown away and no images are scaled down, so every glyph, line and image in the new file is the same as before. The savings are modest, though, and depend a lot on what the file contains.

How it works

pdf-lib loads your PDF and saves it again with the object-streams option on. Object streams were introduced in PDF 1.5 and are defined in ISO 32000. They store a group of indirect objects inside one stream, which is then Flate-compressed with the same deflate method ZIP and PNG use.

Only the document's structure is reorganized and compressed, so text and vector content can shrink noticeably while images that are already compressed stay as they are. The tool compares the new size with the original and reports the saving, or tells you the file was already optimized.

Processing pipeline

  1. Step 1. Add a PDF. It is read into memory on your device and not uploaded.
  2. Step 2. pdf-lib saves the document again with object streams enabled (useObjectStreams: true).
  3. Step 3. Many small objects are packed into Flate-compressed streams, which cuts structural overhead.
  4. Step 4. The new size is compared with the original to measure the saving.
  5. Step 5. The optimized file downloads as compressed.pdf, with a note on how much smaller it is.

Privacy

The PDF is compressed on your device. It is read from disk, re-packed in the page's memory and offered back as a download. No copy goes to NineClip or anyone else.

There is no account and nothing is kept. Close the tab and both files are cleared from memory, so you can use it on confidential documents you would not hand to an online compression service.

Technical details

Enginepdf-lib (open-source, JavaScript)
MethodObject streams (PDF 1.5), Flate-compressed
TypeLossless, no image downsampling
Typical saving~10-25% on text/vector-heavy PDFs
Image-heavy PDFsLittle to no reduction
Outputcompressed.pdf
UploadNone; the PDF stays in your browser

Standards and references

  • ISO 32000 / PDF 1.5: defines object streams (clause 7.5.7), which store many indirect objects in one compressed stream and remove the per-object overhead.
  • DEFLATE (RFC 1951): the lossless Flate compression applied to those streams. ZIP and PNG use the same algorithm.
  • pdf-lib: re-saves the file with object streams enabled, in the browser.

Accuracy and limits

Lossless compression has a limit. The file describes the same content more efficiently, but image resolution and quality are never lowered. The result looks exactly like the original, and only structural overhead can be removed, not picture data.

PDFs made mostly of text and vector graphics, such as reports, contracts and generated documents, usually lose 10-25%. In PDFs that are mostly images, especially scans and photo pages, the images make up most of the size and are left alone, so the file may shrink slightly or not at all. The tool says so when that happens.

The most effective way to shrink an image-heavy PDF is to downsample its images to a lower DPI. That is lossy: it cuts the size but changes the pixels, and this tool does not do it. If a scan has to get much smaller, lower the image resolution before converting to PDF, or compress the images separately first.

Many modern PDFs are already saved with object streams. They have little overhead left, so compressing them again saves almost nothing. That is expected, not a failure.

Where this kind of compression helps

0%10%20%30%Text and vector PDFsabout 10–25%Scans and photo pageslittle to no changeAlready saved with object streamsalmost nothing
The method is lossless. It removes structural overhead and leaves image data as it is.

Real-world uses

Trim a generated report

Cut the structural overhead from a PDF of text and charts exported by a word processor or reporting tool.

Tidy a bloated export

Some apps write PDFs inefficiently. Saving with object streams recovers that space without loss.

Email a text PDF

Get a document-heavy file under an attachment limit without changing how it looks.

Archive without quality loss

Keep a smaller copy that is pixel-identical to the original, with no downsampling.

When it fits, and when it doesn't

Good for

  • Text- and vector-heavy PDFs
  • Shrinking a file without quality loss
  • Cleaning up inefficiently saved files
  • Private documents you cannot upload

Not the best choice for

  • Scans and photo-heavy PDFs (little to gain)
  • Hitting an aggressive size target
  • Files already saved with object streams
  • Reducing image resolution

To make an image-heavy PDF much smaller, lower the DPI of its images or compress the source images, then rebuild the PDF. You will lose some quality in exchange for the smaller file.

Tips and tricks

What we would do

Frequently asked questions

How much smaller will my PDF get?
Text- and vector-heavy files usually lose about 10-25%. Image-heavy or scanned PDFs often shrink very little, because the images make up most of the size and are not altered.
Does compressing reduce quality?
No. The compression is lossless: it re-packs the file's structure and does not downsample images or change any pixels. The compressed PDF looks identical to the original.
Why did my file barely shrink, or not shrink at all?
Either it is image-heavy (this tool doesn't downsample images) or it was already saved with object streams, leaving little overhead to remove. The tool tells you when that is the case.
What are object streams?
A PDF 1.5 feature that packs many of a document's small objects into one compressed stream, so each one no longer carries its own storage overhead. The ISO 32000 standard defines it, and it is lossless.
How do I compress a scanned PDF further?
A scan is made of images, so the thing that helps is downsampling: lowering the images' DPI, which loses some detail. Reduce the image resolution before making the PDF, or compress the images first. This tool won't degrade your scan to hit a size.
Is it lossy or lossless?
Lossless. Nothing is discarded and the same content is stored more compactly, which is why the savings are smaller than tools that downsample images.
Are my files uploaded for compression?
No. pdf-lib re-saves the PDF inside your browser. Nothing is sent to a server, and refreshing the page clears it from memory.
Will it break links, text or fonts?
No. Object-stream compression changes how objects are stored, not what they contain, so text stays selectable and links keep working.
Can I compress the same PDF twice to shrink it more?
Not by much. After one save with object streams there is little structural overhead left, so a second pass saves almost nothing.
Does it work on my phone?
Yes, in any modern mobile browser. Very large files need a lot of the phone's memory, but typical documents compress quickly.

References

This page explains what the object-stream re-save does to your file and names the cases (scans, photo-heavy PDFs, files already optimized) where it saves little.

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