Compress PDF — shrink your PDF without losing content
Drop a PDF below and get a lighter version back. The compression runs entirely in your browser via pdf-lib — your document never leaves your device.
Your file is processed entirely in your browser. Nothing is uploaded.
PDF files accumulate weight from inefficient internal structures — redundant object references, uncompressed metadata streams, suboptimal cross-reference tables. When a PDF has been through multiple editing rounds, merged from several sources, or exported from software that does not optimize its output, the file can be 10 to 40 percent larger than it needs to be without any change to the visible content. That is the waste this tool removes.
This compressor uses pdf-lib to re-serialize your PDF with object-stream compression enabled, which consolidates the internal object graph and applies flate (zlib) deflation to the structure streams. The result is a smaller PDF with identical page content. It is important to be honest about the scope: this is structural compression, not image re-encoding. If your PDF is large because it contains high-resolution photographs, the gains will be modest (5-15 percent) because the images themselves are already compressed. If your PDF is large because of structural bloat (many edits, merged sources, verbose metadata), gains of 20-30 percent are common. For aggressive size reduction on image-heavy PDFs, consider converting to JPG or re-encoding the images at a lower resolution in a dedicated tool.
How to compress a PDF in 4 steps
- 1
Select your PDF file
Drop the .pdf into the dropzone or click to browse. Any readable PDF is accepted.
- 2
Let pdf-lib re-serialize the document
The library loads your PDF, enables object-stream compression, and writes a new, optimized version. Most files finish in under a second.
- 3
Check the size reduction
The result panel shows the original and compressed sizes plus the percentage saved. If the saving is minimal, the PDF was already well-optimized.
- 4
Download the compressed PDF
Save the lighter PDF to your device. The page content is identical to the original — only the internal structure has been streamlined.
What this compression does and does not do
This tool optimizes the PDF’s internal data structures. It consolidates objects into streams, applies flate compression to uncompressed data, and removes redundant cross-reference entries. It does NOT re-encode embedded images at a lower resolution, strip high-resolution image data, downsample fonts, or remove content. The page content, text, images, and annotations you see in the PDF are preserved pixel-for-pixel. The gains come from fixing structural inefficiency, not from degrading content. If you need aggressive compression that does change the images, you would need a tool that re-encodes images at a target quality — something that requires heavier processing and is on our roadmap for a future version.
When should you compress a PDF?
Emailing a PDF that exceeds the 25 MB limit
A 10-30 percent size reduction can push a 30 MB file under the email attachment cap without degrading any content.
Uploading to a portal with a file size cap
Government portals, job sites, and contract systems often cap uploads at 10 or 20 MB. Structural compression may bring your file under the limit.
Reducing storage footprint of a PDF archive
If you store thousands of PDFs, a 15 percent average reduction adds up to significant disk savings over time.
Speeding up PDF downloads on a website
If your site hosts downloadable PDFs, lighter files mean faster downloads and lower bandwidth costs.
Frequently asked questions
- How much smaller will my PDF get?
- It depends on the source. PDFs with verbose internal structures (many edits, merged sources, metadata-heavy exports) typically shrink 15-30 percent. PDFs that are already optimized or that are large purely because of high-resolution images may shrink only 2-10 percent. The result panel shows the exact saving so you can verify before keeping the compressed version.
- Does compression change the visible content?
- No. The text, images, annotations, form fields, and layout of every page are preserved exactly. Only the internal serialization format changes — objects are packed into streams and redundant cross-references are removed.
- Why are the gains modest compared to online tools?
- Server-based PDF compressors (Smallpdf, iLovePDF, Adobe) re-encode the images inside the PDF at a lower resolution, which produces much larger savings but also degrades image quality. Our tool does not touch the images — it only optimizes the document structure, which is lossless. If you need deeper compression, those server-based tools offer it at the cost of uploading your file.
- Can I compress a password-protected PDF?
- The tool tries to open in ignoreEncryption mode, which works for PDFs with an empty owner password. Fully encrypted PDFs that require a user password will fail.
- Is my PDF uploaded?
- No. pdf-lib runs entirely in your browser. The PDF is loaded locally, re-serialized locally, and the compressed output is produced locally. Nothing is ever uploaded.