A PDF that is too big to email or upload is almost always big because of images, not text. A 40-page report exported from Word might be 300 KB, while a 10-page scan of the same kind of document can easily be 20 MB. Knowing why your file is large tells you how far you can shrink it and what you give up in return. Here's how PDF compression really works, and how to hit a size limit without making the document unreadable.
What makes a PDF large?
- Scanned pages. A scanner or phone camera stores each page as one big photograph. At 300 DPI in colour, a single A4 page can be several megabytes before compression.
- High-resolution photos. Brochures, catalogues and presentations often embed images at print resolution, far more detail than a screen can show.
- Embedded fonts. Fonts are usually a small share of the size, unless a document embeds several complete font families.
- Leftovers. Metadata, thumbnails, and unused objects left behind by repeated editing add up.
Lossless vs lossy compression
Lossless compression cleans up the file's structure without changing anything you can see: text stays text, images keep every pixel. It is completely safe, but it rarely saves more than a small percentage.
Lossy compression re-encodes the images at a lower resolution and quality. This is where the big savings are, often 70% to 90% on scanned or photo-heavy files, at the cost of some sharpness. Every online PDF compressor that promises huge reductions is doing some form of lossy compression.
How to compress a PDF for free
- Open the Compress PDF tool.
- Drag your PDF onto the page. The document is processed in your browser, so it never leaves your device.
- Choose a compression level. The page shows your current size and an estimate of the result.
- Press Compress PDF and download the smaller file.
What the three levels do
| Level | What happens | Best for |
|---|---|---|
| Basic | Lossless cleanup: removes metadata and unused data and repacks the file. Text stays selectable. | Text documents, contracts, anything you need to keep searchable |
| Recommended | Re-renders each page as an optimised image at about 108 DPI and 72% JPEG quality. | Scans and image-heavy files that need to be much smaller |
| Extreme | Re-renders pages at about 80 DPI and 50% quality for the smallest possible file. | Strict upload limits where readability on screen is enough |
Two safety nets are built in. If re-rendering doesn't actually make a file smaller (common with text-only PDFs), the tool falls back to the lossless result. And if nothing beats the original, it gives you the original file back rather than a bigger one.
One trade-off to know about: the Recommended and Extreme levels turn each page into an image, so text can no longer be selected, searched or copied. Keep your original if you might need that later.
Which level should you choose?
- A contract, CV or report exported from Word or Google Docs: start with Basic. These files are usually already small, and image compression won't help much.
- Scanned documents, receipts and ID copies: use Recommended. The result is easy to read on screen and fine for most online forms.
- A portal with a 1 MB or 2 MB limit: try Recommended first, then Extreme if the file is still too big.
- Anything you will print: use Basic, or keep the original. Around 100 DPI looks sharp on screen but soft on paper.
Common size limits
| Where you're sending it | Typical limit |
|---|---|
| Gmail attachments | 25 MB (bigger files are sent as a Google Drive link) |
| Outlook.com attachments | 20 MB |
| Yahoo Mail attachments | 25 MB |
| Job, visa, university and government portals | Often 1 MB to 5 MB per file |
Other ways to make a PDF smaller
- Remove pages you don't need. Blank scan backs, cover pages and appendices add weight. Remove Pages deletes them in a few clicks.
- Split the file. If a portal allows several uploads, Split PDF can break one large document into parts. (Going the other way? See how to merge PDF files.)
- Export smaller from the source. In Microsoft Word, File > Save As > PDF offers Minimum size (publishing online), which downsamples images during export.
- Scan smarter. For text documents, scanning at 200 to 300 DPI in greyscale produces much smaller files than 600 DPI colour, with no loss in readability.
- On a Mac: Preview's File > Export dialog has a Reduce File Size Quartz filter. It works, but it can be very aggressive with images, so check the result.
Why won't my PDF get any smaller?
If even the stronger levels barely help, the file is probably already well optimised: a text-only document, or a PDF that was compressed before. Heavy vector artwork (detailed maps, CAD drawings) can also resist compression, because the size comes from the drawing instructions rather than from images. In those cases, removing pages or splitting the file is the only real option.
Frequently asked questions
Does compressing a PDF reduce quality?
Lossless (Basic) compression doesn't change anything you can see. Lossy levels reduce image resolution and quality; on screen the difference is usually minor, but printouts can look softer.
Can I compress a PDF to under 1 MB?
Usually, for documents of up to a few dozen scanned pages. Try the Recommended level first and Extreme if needed; for very long scans, you may also need to split the file.
Is it safe to compress confidential PDFs online?
Many services upload your file to their servers. The Quickaboo compressor runs entirely in your browser, so the document stays on your device.
Why can't I select text after compressing?
The Recommended and Extreme levels convert pages into images to save space. Use the Basic level, or keep the original, when you need selectable text.