Free Compress PDF Online
Reduce your PDF file size instantly — no upload, no account, runs entirely in your browser.
PDF compression reduces file size by stripping embedded metadata, revision history, creator information and redundant data that accumulates in PDFs from various applications. The result is a leaner file that attaches faster in emails, uploads quicker to cloud services and takes less storage — without any visible change to content, fonts or images. Everything runs in your browser using pdf-lib.
Click to select or drag & drop your PDF here
How it works
Open your PDF
Text-heavy documents shrink most; scans have little left to remove.
Metadata and objects repacked
Unused entries are dropped and the internal structure rewritten.
Download the smaller file
The size before and after is shown, so you can see whether it helped.
How Does PDF Compression Work?
PDF compression reduces file size by stripping embedded metadata — author names, keywords, creation tools, revision history and other hidden data that adds weight without adding value. OneConvert uses pdf-lib with object stream compression (equivalent to PDF/1.5 compression) to pack the remaining data more efficiently.
Results vary by PDF: documents heavy with metadata can shrink significantly, while already-optimised PDFs may see smaller reductions. Image-heavy PDFs require deeper compression (resampling images) which is a server-side operation. For those, use our compress tool to remove metadata first, then open in your PDF viewer to reduce image quality.
What This Compressor Can and Cannot Do
Being explicit about the mechanism matters more than a percentage claim. This tool does two things: it strips document metadata (title, author, subject, keywords, producer, creator) and it rewrites the file using object streams, which packs many small PDF objects into a single compressed stream instead of storing each separately. Both are lossless. Nothing in the visible content is altered or re-encoded.
That mechanism explains where it works and where it does not. Text-heavy documents with many small objects — reports, exports from word processors, forms, generated invoices — often shrink meaningfully, because they contain exactly the kind of object overhead that object streams compress. Files already written with object streams by a modern producer will barely move, since the work is already done.
Scanned documents are the honest exception. A scan is essentially one large JPEG per page, and the bulk of the file is that image data. This tool does not re-encode images, so a scanned PDF will shrink by a fraction of a percent at best. If you need a scan to get smaller, the only real lever is re-encoding the images at lower quality or resolution, which is a lossy operation and outside what this tool does. Rather than quietly delivering a disappointing result, it is worth knowing this before you upload a 40 MB scan and wonder why it came back at 39.8 MB.