A 20 MB PDF that refuses to attach to an email is one of the small daily frustrations of modern work. The good news: most oversized PDFs can be shrunk dramatically without any visible loss in quality. This guide explains why PDFs get so big, how compression actually works, and how to get the smallest possible file while keeping your text crisp and your images clear.
Compress a PDF in three steps
- Open Compress PDF.
- Drop in your file.
- Click Compress PDF and download the smaller version.
Like our other core tools, compression runs in your browser, so your document is never uploaded anywhere.
Why do PDFs get so big?
A PDF is essentially a container. When it balloons in size, it's almost always because of one of these:
- High-resolution images. A single full-page scan at 600 DPI can weigh several megabytes. Multiply that across a 30-page document and you have a monster file.
- Embedded fonts. PDFs bundle the fonts they use so they render identically everywhere. That's great for consistency but adds weight.
- Redundant data and metadata. Editing history, thumbnails, unused objects and bloated metadata all pile up, especially in files that have been exported and re-exported several times.
Understanding the cause helps you pick the right fix.
Lossless vs lossy compression
There are two broad ways to make a PDF smaller:
- Lossless removes waste — redundant objects, unnecessary metadata, inefficient structure — without touching how the document looks. The result is identical on screen but lighter. This is always safe.
- Lossy re-encodes images at a lower resolution or quality. This can shrink scan-heavy PDFs enormously, and if done sensibly (say, targeting 150 DPI for screen reading) the difference is invisible to the human eye.
The trick to "compressing without losing quality" is to apply lossless optimization aggressively and lossy image compression only as much as the document can take before you'd notice.
Getting the smallest possible file
- Remove pages you don't need first with Remove Pages or the visual Organize PDF editor. Fewer pages, smaller file.
- Right-size your scans. For anything meant to be read on a screen, 150–200 DPI is plenty. Higher resolutions only matter for large-format printing.
- Export images separately if you only need the pictures — PDF to JPG can be far smaller than a full PDF.
- Avoid re-compressing. Compressing an already-compressed file repeatedly won't help and can degrade quality. Start from the cleanest original you have.
When you should not compress
If your PDF is destined for a professional print shop, a legal filing that requires original fidelity, or archival at full resolution, keep the uncompressed version. Compression is about convenience — email, uploads, sharing — not about replacing your master copy. A good habit is to keep the original and compress a copy.
Compression vs other approaches
Sometimes compression isn't the right tool at all:
- If the file is large because it has too many pages, splitting it with Split PDF may serve you better.
- If you only need to send a few pages, extract just those with Extract Pages.
- If the problem is an enormous single image, resize the image before putting it into the PDF.
Troubleshooting
The file barely got smaller. It was probably already well-optimized, or its size comes from text and fonts rather than images — there's less to squeeze there.
The images look soft now. You compressed too aggressively. Re-do it from the original with a gentler setting.
It won't open after compression. Make sure you're starting from a valid, non-corrupted source file.
Frequently asked questions
Will compressing change how my PDF looks? With sensible settings, no — text stays sharp and images stay clear. Only very aggressive settings on image-heavy files become noticeable.
Is it free? Yes, and there's no watermark.
Are my files uploaded? No. Compression happens in your browser.
Try it now: Compress PDF →