How to compress a PDF so it fits in an email

Published September 28, 2026 by the ModifyPDF team

You finish a document, attach it to an email and get a bounce: the file is too large. PDFs that contain scans or photos can easily run to 30, 50 or 100 MB, while most email services cap attachments far lower. This guide explains where the size comes from and how to bring it down without making the document unreadable.

How big can an email attachment be?

Limits vary by provider and change from time to time, but these are the common ceilings:

Gmail: 25 MB in total per message. Larger files are offered as a Google Drive link instead.
Outlook.com and Microsoft 365: around 20 MB for Outlook.com; business accounts are often set to 20–35 MB by the administrator.
Yahoo Mail: 25 MB.
Company mail servers: frequently 10 MB, sometimes less.

Attachments are encoded for transport, which adds roughly a third to their size, so a 20 MB PDF can count as nearly 27 MB. As a rule of thumb, aim for under 10 MB if you don’t know the recipient’s limit.

Why is my PDF so big?

Text is tiny. A 200-page novel set in normal fonts is often under 2 MB. What makes PDFs heavy is almost always images:

Scanned pages. Every page of a scan is a full-page photograph. Scanners set to 300 or 600 dpi in color produce several megabytes per page.
Phone photos. A modern phone camera takes 12–50 megapixel images. Dropped into a report at the size of a postcard, most of those pixels are wasted.
Exports from design tools that keep print-resolution images even when the document is only going to be read on screen.

What compression actually does

Good PDF compression leaves text, fonts and vector graphics alone and works on the images. There are two levers:

Resampling lowers the number of pixels in each image to match the size it is actually displayed at. A photo printed 10 cm wide needs about 600 pixels across at 150 dpi, not 4,000.
Re-encoding saves the image again as a JPEG at a chosen quality level.

In ModifyPDF’s Compress PDF tool, Recommended resamples images to 150 dpi at their printed size, which looks sharp on screen and in ordinary office printing. Extreme goes down to 72 dpi for the smallest possible file, which is fine for reading on a screen but visibly soft when printed. Less compression keeps full resolution and only re-encodes images at high quality. Because text is untouched, it stays crisp and searchable at every level.

Step by step

Open Compress PDF and choose your file. It is processed in your browser; nothing is uploaded.
Start with Recommended and download the result.
Check the new size. If it is still too big, run the original again with Extreme.
Open the compressed file and zoom in on a photo or a small printed detail, such as a signature or a table, to make sure it is still legible.

When compression isn’t enough

If a file is still over the limit after extreme compression, it is usually just long. Two options work well:

Split it. Split PDF has a fixed-size mode that cuts the document into equal chunks of a set number of pages, so you can send it across two or three emails.
Send a link. Upload the file to a cloud drive you already use and share a link instead of an attachment.

Why a text-only PDF barely shrinks

If your document is mostly text, compression may only save a few percent. That isn’t a fault: there is simply nothing heavy to remove. Fonts and text are already stored efficiently, and squeezing them further would risk damaging the file. If a text document is surprisingly large, check whether it contains a high-resolution logo or background image on every page.

Tips for smaller PDFs from the start

Scan documents at 200 dpi in grayscale unless you really need color. Text stays perfectly readable.
Resize photos before placing them into a Word or Google Docs file.
When exporting from Word, choose the “Minimum size” or “Online publishing” option if you only need the file for screens.