How to make a PDF smaller to email or upload

A PDF over the limit bounces back, or the upload form refuses it. Text takes very little room: a long report that is only text can be well under 1 MB. A big PDF is almost always big because of scanned pages or photos, and those are what can be made smaller.

1. Find the limit you have to meet

Leave some room. Email turns attachments into text on the way, which makes them about a third bigger, and the receiving mail server can have a lower limit than yours: some company servers accept 10 MB or less. A PDF under about two thirds of the limit is safe.

2. Shrink the scans and photos inside

1. Open Compress PDF and set the size it has to fit: pick 1 MB, 500 KB, 200 KB or 100 KB, or type your own.
2. Choose the PDF. Your browser saves each image in it again at the highest quality that lets the whole file fit. Text, fonts, links and form fields stay as they are, and the text stays selectable. Nothing is uploaded.
3. Check the new size, download it, and open it to make sure scanned pages are still easy to read.

If the PDF is mostly text, there is little to remove, and the page says so. Sizes there count 1 MB as 1,000,000 bytes, so a file under the limit is also under it on sites that count 1 MB as 1,048,576 bytes.

3. Still too big? Flatten a scanned document

When even small images don't fit, Compress PDF offers to flatten the pages: each page becomes one picture, made as sharp as the size allows. That reaches much smaller sizes, but the text can no longer be selected or searched, and links and form fields stop working. It suits a signed scan or a receipt, not a form someone still has to fill in.

4. Or send less

• Remove pages nobody needs, like blank scans, cover sheets or appendices, with Organize PDF.
• Split it into parts that each fit, by page ranges or into equal parts, with Split PDF, and send them in separate emails.
• Send a link instead. Gmail, Outlook.com and iCloud Mail offer this themselves for big attachments. The file is then stored on that company's servers, which is worth knowing for private documents.

What doesn't help much

• Zipping the PDF. The images inside a PDF are already compressed, so a ZIP is usually only a little smaller, and many upload forms don't accept ZIP files.
• Scanning at high settings. If you are scanning the pages yourself, 150 to 200 DPI in greyscale is plenty for letters and forms. 600 DPI in colour makes each page many times bigger without making it easier to read.