How to compress a PDF for email
By M Alamgir Saeed · Updated
You attach a PDF, press send, and the email bounces back: the file is too big. It happens all the time with scanned contracts, photo-heavy reports and brochures. This guide explains why it happens, how big an attachment can be, and how to make a PDF small enough to send without turning the text into a blurry mess.
How big can an email attachment be?
Every email service sets its own limit. Gmail and Yahoo Mail accept attachments up to 25 MB per message, and Outlook.com allows about 20 MB. Many company mail servers are stricter and stop at 10 MB, and the person receiving the email may have a lower limit than you do.
There is a second catch: email does not send files as they are. Attachments are encoded as text before they travel, which makes them roughly a third larger. A 19 MB PDF can therefore be rejected by a 25 MB limit. To be safe, aim for a PDF under about 10 MB, and under 5 MB if you are sending it to a large company or a government office.
| Email service | Attachment limit | Safe PDF size |
|---|---|---|
| Gmail | 25 MB | under 15 MB |
| Yahoo Mail | 25 MB | under 15 MB |
| Outlook.com | about 20 MB | under 12 MB |
| Many company servers | often 10 MB | under 5 MB |
Why is my PDF so large?
Text takes up very little space. A 50-page report that contains only text is usually well under 1 MB. What makes a PDF heavy is images: scanned pages, photos, screenshots and high-resolution graphics. A single page scanned at high resolution can be several megabytes on its own.
That is good news, because it means compression should focus on the images and leave the text alone. Shrinking the pictures to a sensible resolution for a screen usually removes most of the size, while the words stay perfectly sharp.
How to compress a PDF step by step
The Compress PDF tool on this site works entirely in your web browser, so the document is never uploaded anywhere. That matters for contracts, invoices, medical letters and anything else you would rather not hand to a stranger's server.
- Open the Compress PDF tool and drop your file onto the page (or click to choose it).
- Pick Recommended mode first. It re-compresses the photos inside the PDF and keeps the text as real, selectable text.
- Download the result and check the new size shown on the page. If it is now small enough, you are done.
- If the file is still too big, try Strong mode. It turns each page into an image at the resolution you choose, which gives the smallest file, but the text can no longer be selected or searched.
- Open the downloaded PDF once before you send it, to make sure every page still looks right.
Which compression setting should I choose?
Use Recommended mode for anything people will read on screen and might want to copy text from: reports, CVs, forms and contracts. It only touches the images, so headings, tables and small print stay crisp.
Use Strong mode for scanned documents, where every page is already a picture, and for photo-heavy brochures that only need to look right. A resolution of 150 DPI is a good balance for reading on a screen; 100 DPI or lower is fine for a quick preview but small print may become hard to read.
If a PDF contains no photos at all, compression will not help much, because there is nothing heavy to shrink. In that case the tool keeps your original file and tells you so, instead of handing you a "compressed" copy that is not actually smaller.
Still too big? Other ways to send a large PDF
Some documents are simply huge, such as a 300-page scanned book. You still have good options.
- Split it into parts with Split PDF and send two or three smaller emails.
- Send only the pages that matter: remove the rest with Delete PDF Pages.
- Share a link instead of an attachment, using a cloud drive such as Google Drive, OneDrive or Dropbox.
- Avoid zipping the PDF. PDF files are already compressed internally, so a ZIP archive usually saves almost nothing.
Is it safe to compress a PDF online?
It depends on the website. Many online compressors upload your file to their servers, process it there and keep it for a while. With a browser-based tool like this one, the work happens on your own computer or phone and the file never leaves your device. You can check this yourself: open your browser's developer tools, choose the Network tab and compress a file, and you will see that the PDF is not sent anywhere.
If a PDF is confidential, you can also add a password with Protect PDF after compressing it. Send the password separately, for example by text message, not in the same email.
Frequently asked questions
Does compressing a PDF reduce its quality?
Only the images are affected. In Recommended mode text stays sharp and selectable; photos become slightly softer, which is rarely visible on screen. Strong mode turns pages into images, so choose a resolution of around 150 DPI if the document has small print.
What size should a PDF be for email?
Under 10 MB is safe for most services, and under 5 MB if you are sending to a company or government address, because their mail servers often have lower limits than Gmail or Outlook.com.
Why is my compressed PDF not smaller?
The PDF probably contains mostly text and vector graphics, which are already compact. There is nothing heavy to shrink, so the original is the best version to send.