How to compress a PDF
Last updated: September 3, 2026
If a PDF is too big to email or upload, compressing it is the fix, but what 'compress' really does depends on what is taking up the space. Here is what actually shrinks a file, the honest trade-off involved, and how to get the smallest result without wrecking it.
Use our free Compress PDF tool. It runs in your browser.
Where the megabytes actually live
Open almost any oversized PDF and the bulk of it is raster images: scanned pages, embedded photos, product shots, or high-resolution screenshots. The text layer of a long report might be only a few dozen kilobytes, while a single full-page scan can be several megabytes on its own. That imbalance is the key to compression: shrink the images and you shrink the file. Leave them alone and no amount of tweaking moves the needle much.
This is why a 40-page contract that is pure text is often already tiny, while a three-page brochure full of photography is enormous. Knowing which kind of document you have tells you in advance how much you can expect to save.
Compressing your PDF step by step
- Open the Compress PDF tool.
- Drag your PDF onto the drop zone, or click to browse for it.
- Pick a level: Light preserves the most detail, while Strong pushes for the smallest possible file.
- Press Compress PDF. Each page is re-rendered as an optimized JPEG and rebuilt into a new document.
- Download the result and check the reported size before you send it on.
The trade-off, stated plainly
Our compressor works by re-rendering every page as an optimized image and reassembling the PDF from those images. This is lossy: it throws away image detail you are unlikely to notice in order to save space, and it is extremely effective on scans and photo-heavy files. The cost is real, though: once a page becomes a picture, the text on it is no longer selectable or searchable, and a screen reader can no longer read it aloud. For a scanned receipt you are emailing to an accountant, that is a fine bargain. For a contract someone needs to copy clauses out of, it is not.
When to reach for a different tool
Lossy compression is one of three related jobs, and picking the right one saves you frustration:
| Tool | What it does | Keeps text selectable? | Best for |
|---|---|---|---|
| Compress PDF | Re-renders pages as images (lossy) | No | Scans and photo-heavy files you just want smaller |
| Optimize PDF | Rebuilds internal structure (lossless) | Yes | Text documents bloated by messy saving |
| Reduce File Size | Steps down until it hits a target you set | Not at aggressive targets | Meeting a hard limit like "under 2 MB" |
If you need selectable text and only modest savings, start with optimizing. If a form demands a specific number, the reduce-to-target approach is purpose-built for it.
Real situations where this shines
- A scanned ID or bank letter that a portal rejects for being over the size cap: Strong compression usually clears it instantly.
- A slide deck exported as PDF with large background photos, ready to attach to an email that keeps bouncing.
- A photo-rich catalogue or menu you want to host or share, where visitors care about load speed more than pixel-perfect zoom.
Why a file sometimes barely budges
If your PDF is already small, already well-compressed, or made almost entirely of text and vectors, there simply is not much redundancy left to squeeze out. Rather than hand back a file that is the same size or even larger, the tool is upfront about it and tells you when it cannot help. That honesty is deliberate: a compressor that silently inflates your file is worse than one that says "this is already about as small as it gets."
Frequently asked questions
Does compressing reduce quality every time? It reduces image quality; how visible that is depends on the level and the content. Light is often indistinguishable on screen; Strong can soften photos noticeably when you zoom in.
Can I compress the same PDF twice? You can, but re-compressing an already-compressed file mostly adds artefacts for little extra saving. It is better to start from the original and pick a stronger level once.
Is there a page limit? Up to 100 pages, because all the rendering runs on your own device's memory rather than a server.
Will compression change my page dimensions? No. Pages keep their size and aspect ratio; only the image data inside them is re-encoded.
What if I need selectable text and a smaller file? Optimize first for a lossless trim, and only compress if the size is still driven by large images you can afford to soften.
Privacy for your documents
Compression happens completely inside your browser tab: the PDF is read from your disk, re-rendered in memory, and written back out without a single byte being sent to us. For scanned IDs, medical letters, or financial statements, that means the sensitive content never travels the network at all. If you want the fuller picture, read are online PDF tools safe.