How to compress a PDF for email and upload limits

By the LambiPdf team · Updated 1 November 2026 · 6 min read

Email services and upload forms set size limits, commonly somewhere between a few megabytes for job portals and around 20–25 MB for email attachments. A scanned contract or a brochure full of photos can blow past that easily. Here is what makes a PDF large and the options you have for shrinking it.

What makes a PDF big

Text costs almost nothing: a hundred pages of plain text can fit in a few hundred kilobytes. File size comes from images:

• Scans and phone photos. Every scanned page is a full image. A 20-page scan at high resolution can easily reach tens of megabytes.
• High-resolution pictures in brochures and presentations, often far sharper than any screen needs.
• Embedded fonts add a little, especially with several fonts or large character sets.

So compression is almost entirely about images.

How LambiPdf compresses a PDF

LambiPdf’s Compress tool re-renders each page at a lower resolution and saves it as a compressed image. It has three levels:

• Light. Small reduction, best quality. Use it when the document must stay crisp, such as plans or detailed diagrams.
• Recommended. A balance that keeps ordinary documents readable on screen and in print.
• Maximum. The smallest file. Fine for reading on screen; small print may get soft.

One trade-off matters: because pages are re-rendered as images, their text is no longer selectable or searchable after compression. For a scan that was already an image, you lose nothing. For a text document such as an exported report, compression can make the file bigger and remove its text, so try the options below first.

Use Preview before saving, and zoom in on the smallest text you need to read.

Other ways to fit under the limit

1. Remove pages nobody needs. Blank pages, duplicate scans and appendices the recipient didn’t ask for. Use Delete pages.
2. Split the file. Send a long document as two or three attachments with Split PDF, or extract only the pages that matter.
3. Convert to grayscale. Color scans of black-and-white documents carry color information nobody needs. Grayscale PDF removes it.
4. Rescan at a sensible resolution. 300 dpi is enough for text; 600 dpi roughly quadruples the data for little visible gain.
5. Share a link. For very large files, a link from your own cloud storage avoids attachment limits altogether.

Check the result

After compressing, open the output and read a page at normal size, then zoom in on signatures, stamps and the smallest numbers. If anything important is hard to read, go back one level. Your original file is untouched, so you can always try again.

Compressing privately

The files people compress for email are often the ones being sent to a bank, a landlord or an employer, so they contain personal details. LambiPdf compresses in your browser, without uploading the PDF.

Questions people ask