You attach the PDF, hit send, and get a bounce: "message too large." It usually happens at the worst moment, with a contract, an application or an invoice due in minutes. The fix takes about a minute once you know what is actually making the file heavy.

What the limits really are

Gmail and Yahoo allow attachments up to 25 MB. Outlook.com and iCloud Mail sit closer to 20 MB. Plenty of company mail servers set their own cap, often 10 MB. Email also inflates attachments by roughly a third when it encodes them for sending, so a 20 MB PDF can fail even on a 25 MB limit. As a rule of thumb, aim for under 10 MB if you don't know the recipient's server.

Why your PDF is so big

Almost always it is images. A scan or a photo-heavy export stores each page as a large picture, while a text-only PDF of 50 pages can be a few hundred kilobytes. Embedded fonts and leftover editing data add a bit, but images are the main cause. That tells you where to look: shrinking the images is what actually saves space.

Step by step

1. Open Compress PDF and upload your file (up to 50 MB).
2. Pick a level. Low keeps the most quality, Medium is the sensible default, and High squeezes hardest.
3. Download the result and compare the size with the original.
4. Zoom into a page with small print or a signature to check it is still readable before you send it.

Start on Medium. Only move to High if the file is still too big, because High is where fine detail can start to soften.

If it is still too large

• Remove pages nobody needs. Cover sheets and blank scan pages add up. Delete Pages takes them out.
• Split the document. Send a 60-page file as two 30-page parts with Split PDF, then mention both attachments in your message.
• Convert to grayscale. A colour scan of a black-and-white document carries colour data you don't need. Grayscale PDF reduces it.
• Share a link instead. For anything truly large, upload it to your cloud storage and send the link.

How to avoid the problem next time

When you scan, choose 150 to 200 DPI for ordinary documents instead of 300 or 600, and pick black and white for text-only pages. Exporting from Word or Google Docs directly to PDF, rather than printing to a scanner and back, also keeps files small. If you regularly send batches, Batch Compress handles several files in one go.

Mistakes to avoid

• Compressing repeatedly. Each pass can soften images a little more. Go back to your original if the result isn't right.
• Compressing before merging. Merge first, then compress once.
• Not checking the result. Zoom in on small print before you send.
• Sending big files unannounced. A short note to the recipient saying the file is large helps if it gets filtered.

Frequently Asked Questions

Will compressing my PDF make the text blurry?

Text in a normal PDF is stored as vector data and stays sharp. Compression mostly affects the images. On Medium, most documents look the same on screen.

How small can I realistically get a PDF?

It depends on the content. A text document shrinks a little because it is already small. A scanned document full of full-page images can drop dramatically. Photo-heavy files sit in between.

Is it safe to compress a confidential file online?

Files are uploaded over an encrypted connection and deleted automatically after processing. If a document is highly sensitive, check your organisation's policy before uploading it to any online service.

My PDF is under 25 MB but still bounced. Why?

Encoding overhead, other attachments in the same message, or a stricter limit on the recipient's server. Try getting it under 10 MB.