How to Reduce PDF File Size Without Losing Readability

Email providers cap attachments around 20–25 MB, and many upload forms stop at 5 or 10 MB. A PDF that's too big usually isn't big because of its text. Knowing where the bytes come from tells you how to remove them.

What makes a PDF large

• Photos and scans. A single phone photo of a page can be 3–5 MB. A 20-page scan quickly reaches 50 MB or more.
• Images at print resolution. Graphics exported at 300–600 DPI look no better on a screen than at 150 DPI.
• Embedded fonts. Full font files add hundreds of kilobytes; subsets add much less.
• Duplicated resources. Merged or edited PDFs sometimes carry the same image or font several times.

Plain text is small. A 100-page text-only PDF is often under 1 MB.

Shrinking a PDF in the browser

1. Open the PDF compressor and drop in your file. It's processed on your device, which matters for contracts, IDs and medical documents.
2. Start with the lossless option. It removes unused data and rewrites the file compactly, while text, links and images stay exactly the same. For PDFs made in Word or similar, that alone can help.
3. If the file is still too big, recompress the pages: pick a resolution (100–150 dpi reads well on screen, 200 for printing), a JPEG quality around 60–75, and optionally grayscale for scans of black-and-white documents.
4. Check the result: zoom into a page with the smallest text or a signature to make sure it's still legible.
5. Download the compressed PDF.

Why 150 DPI is the sweet spot

DPI (dots per inch) describes how many image pixels cover one inch of the page. Screens show around 100–150 pixels per inch at normal zoom, so images above that are mostly invisible detail. Reducing a 300 DPI scan to 150 DPI removes three quarters of the pixels, and the page still looks sharp when reading. For documents that will be printed professionally, stay at 300 DPI.

When compression isn't enough

• Remove pages you don't need. Use Organize PDF to delete blank pages, cover sheets or appendices.
• Split the document. Split PDF turns one large file into several that each fit a limit.
• Rescan in grayscale. A color scan of a black-and-white letter is three times the data it needs.

Built-in alternatives

• macOS Preview: File → Export → Quartz Filter → Reduce File Size. It's aggressive and can make images blurry.
• Microsoft Word: when saving as PDF, choose Minimum size (publishing online).
• Adobe Acrobat (paid): Reduce File Size or Optimize PDF.

A quick checklist before sending

• Is the text still crisp at 100% zoom?
• Are signatures and stamps readable?
• Is the file under the limit with some margin? Some systems count megabytes differently.
• Did you keep an uncompressed original?

Frequently asked questions

Why did my PDF get bigger after compressing? If a PDF contains only text and vector graphics, rendering pages as images can make it larger. Use the lossless option for such files, or keep the original.

Will text still be searchable? With lossless optimization, yes. When pages are recompressed as images, the text becomes part of the image, and copy-and-paste or search may no longer work. Keep that in mind for documents people need to search.

Can I compress a password-protected PDF? You need to open it with its password first. Afterwards you can protect the compressed version again.

What size should I aim for? For email, stay well under 20 MB. For online forms, read the limit carefully: some mean 5 MB per file, others 5 MB in total.