How to make a PDF small enough to email

Smaller than you might think. Gmail's help pages put the limit for personal accounts at 25 MB, and turn anything larger into a Google Drive link. Microsoft's support pages say its Outlook desktop app limits messages on internet accounts, such as Outlook.com and Gmail, to 20 MB, counting the attachment and the email together, and sets 10 MB by default for business Exchange accounts. Upload portals for job applications, insurance claims and government forms often set lower limits of their own.

Then there is encoding. Email carries attachments as Base64 text, which Microsoft's Exchange documentation says makes a message about 33 percent larger in transit, so a 19 MB PDF can reach a mail server as a message of around 25 MB. Aim for a file comfortably under the limit, not just under it.

Almost always, the images. A PDF of typed text weighs little, because its words are stored as characters and fonts. What makes one heavy is full-resolution photos pasted into a report, or a scanner that saved every page as a large color picture. The right fix depends on which kind you have.

• A document made on a computer, with text you can select: shrink the images inside it and leave the text alone.
• A scan, where every page is already a picture: rebuild each page as a smaller image.

1. Open Compress PDF and drop the file in. Keep text is selected to start. Compress PDF
2. Leave Largest image side at 2000 pixels, or drop it to 1500 or 1000 for a smaller file. A photo filling a US Letter page at 2000 pixels still prints at about 180 DPI.
3. Set the JPEG quality for the photos it rewrites. It starts at 0.72, which is hard to tell from the original; below about 0.50, blocks start to show in smooth areas.
4. Check the preview, which shows the largest photo re-encoded at these settings with its size before and after, then press Compress PDF and download the result.

Text, fonts, links, form fields and bookmarks come through exactly as they were, and charts and screenshots inside the PDF are repacked without loss, and scaled down only if they are larger than the largest image side, so their edges stay sharp. If the images cannot be made meaningfully smaller, the tool says there is nothing smaller to download, rather than handing back the same file under a new name.

Switch Compress PDF to Rasterize pages. Every page is redrawn as an image at the resolution you pick, from 72 to 300 DPI with 150 to start, and saved as a JPEG at the quality you set. Turning on grayscale takes a scan of black text on white paper down a long way, and color it never had is not lost.

This mode turns each page into a picture, so the text in the result cannot be selected, searched or read aloud by a screen reader, and links, form fields and bookmarks go with it. That is no loss for a scan, which had no text layer to begin with, but keep the original of any document that did.

For a document in Keep text, lower the largest image side first, because fewer pixels save more than a lower quality does, then lower the quality, and compress again until the result fits under the limit with room to spare. For a scan in Rasterize pages, the Projected figure comes from a real encode of one page, scaled by the area of the others: turn on grayscale if the pages are black and white, then lower the resolution a step at a time until the projection fits, checking the smallest text on the preview each time.

• Send fewer pages. Organize PDF pages deletes the ones nobody asked for, and removing a page removes its images too.
• Split it. Split PDF cuts the file into ranges, or into chunks of a set number of pages, which can go in separate emails.
• Share a link instead. For a file that has to stay whole and large, a link to cloud storage avoids the attachment limit altogether, and Gmail does this for you above 25 MB.

What does not help is zipping it. The images inside a PDF are already compressed, so a ZIP of a PDF is barely smaller, if at all.