How to reduce a PDF’s size for email

If a PDF is too big to attach, make a smaller copy with Compress PDF: try Optimize first, and switch to Image-based mode if the file is a scan or full of photos. Check the copy is still readable, then attach it. The tool is free, needs no account, and processes the file in your browser.

How big can an email attachment be?

Each provider sets its own limit. Personal Gmail accounts can send up to 25 MB of attachments per message, and anything larger is turned into a Google Drive link. Outlook.com allows 25 MB for the whole message, including the text. The Outlook desktop app has a default 20 MB attachment limit for internet accounts such as Gmail and Outlook.com. Work and school accounts use limits set by their administrator, which can be lower.

There is also a hidden cost. Email encodes attachments as text, which adds about 33% to their size in transit, so a file that looks just under a limit can still be rejected by the receiving server. As a rule of thumb, aim for under 10 MB when you send to an organization you do not know.

You do not need to look up the size first. After you choose a file in Compress PDF, its size appears next to the file name.

Step by step: compress a PDF with PDFReadyGo

The tool accepts one PDF of up to 30 MB at a time and works the same in a browser on Windows, Mac, iPhone and Android.

1. Open Compress PDF.
2. Select Choose a PDF, or drag the file onto the drop area.
3. Under Compression mode, leave Optimize — keep page content selected.
4. Select Compress PDF →. The result shows the before and after size.
5. If the saving is too small, select Start over and choose the same file again.
6. Under Compression mode, choose Image-based — for scans and photos.
7. Under Image quality, choose Balanced · about 110 DPI.
8. Select Compress PDF → again.
9. Select Download result ↓ and save the file before you leave the page.

Which mode should you use?

Optimize is the safe choice for documents created on a computer, such as reports, invoices, forms and exported slides. Nothing on the page changes, so text stays selectable and searchable. It does not shrink photographs inside the file, so the gain is often modest.

Image-based mode redraws every page as a compressed JPG picture, which is where scans shrink. We ran both modes on the live tool on October 29, 2026, using two test files. A five-page text PDF of 3.1 KB came out 39% smaller with Optimize, while Image-based mode would have made it larger, so the tool returned the original. A six-page, 15.3 MB test PDF made of full-page scan-style images gave these results:

• Optimize: 15.3 MB, effectively no change
• Image-based, Higher quality · about 150 DPI: 3.02 MB, 80% smaller
• Image-based, Balanced · about 110 DPI: 1.41 MB, 91% smaller
• Image-based, Smaller · about 80 DPI: 720 KB, 95% smaller

Your own files will give different numbers, but the pattern is typical: scans shrink a lot, and the lowest setting is rarely needed for email. Image-based mode has real costs. Searchable text, links, form fields and accessibility structure are removed, and a digital signature will no longer be valid. For a form someone must fill in or a document that has been signed electronically, stay with Optimize. Image-based compression handles up to 100 pages at once.

What if it does not work?

The file did not get smaller. Some PDFs are already compressed efficiently, and a short text document can grow when turned into page images. If the new version would be bigger, PDFReadyGo gives you the unchanged original, named pdfreadygo-original.pdf, with the message “No size reduction was possible with this setting.” That is an honest outcome, not an error. Why your PDF will not get smaller explains the reasons.

The tool says the PDF is password-protected. Save a copy without the password from the app you normally open it with, if you have permission, and compress that copy.

The file is still over the limit. Reduce what you send instead of squeezing harder:

• Send only the pages that matter. Split PDF extracts a page range, and Organize PDF removes blank pages and appendices.
• Split a long document into two emails and label them “1 of 2” and “2 of 2”. Merge or split? covers when each makes sense.
• If the PDF was made from phone photos, rebuild it from smaller photos with Images to PDF, then compress it.
• Share a cloud storage link instead of an attachment, and check the recipient can open it without an account.

Check the copy before you send it

Open the compressed file and zoom in on the smallest text, tables, signatures, stamps and figures. If anything is blurry, run it again with Higher quality · about 150 DPI. Compression creates a new copy and never changes the original on your device, so keep the original until the email has been received.

Quick answers

Is the file uploaded? No. Compress PDF reads and rewrites the file in your browser, and the document is not sent to our servers. See how privacy works and the FAQ.

Can I combine several PDFs into one small attachment? Yes. Merge them first with Merge PDF, then compress the merged file. On a phone, follow how to combine PDFs on iPhone or Android.

Will the recipient notice? With Optimize, no: the pages are identical. With Image-based mode at Balanced or Higher quality, most documents look the same on screen, but the text cannot be selected or searched.

Email limits checked October 29, 2026.

Related tools

• Compress PDF: make a smaller copy for email or upload portals.
• Split PDF: send only the pages you need.
• Merge PDF: combine attachments into one file before compressing.