How to Make a PDF Small Enough to Email
"Attachment too large" usually appears at the worst moment – just before a deadline. The good news is that most oversized PDFs can be brought under the limit in a few minutes once you know what is making them big. This guide walks through the fixes in the order that loses the least quality.
First, know the real limit
Attachment limits vary by provider and change from time to time, so check your own provider's help pages. At the time of writing, typical figures are:
- Gmail and Yahoo Mail: up to 25 MB of attachments per message.
- Outlook (desktop and Outlook.com): around 20 MB for regular attachments.
- Company mail servers: set by the administrator, often 10 MB or less.
Two details catch people out. First, the limit that matters is the lowest one along the way: your 25 MB Gmail attachment will still bounce if the recipient's company server accepts only 10 MB. Second, attachments are converted to text (Base64 encoding) for transport, which makes them roughly a third larger. Because many servers measure the whole encoded message, a 25 MB limit in practice leaves room for about 18 MB of files. When you don't know the recipient's limit, aiming for less than 10 MB is a safe choice.
Step 1: find out what makes the file big
Divide the file size by the number of pages. As a rough guide, a page of ordinary text needs only a few dozen kilobytes, while a full-color scan of the same page at 300 DPI can easily take one or two megabytes. So:
- Well under 100 KB per page: the file is mostly text. It is probably large only because it has many pages.
- Hundreds of KB or more per page: images dominate – scans, photos, screenshots or high-resolution graphics. Shrinking them is where the real savings are.
- A few pages that are huge: scroll through the document; often a single embedded photo or poster-sized image is responsible for most of the size.
Also check whether the PDF is a scan: if you cannot select the text in your viewer, every page is an image.
Step 2: try a lossless re-save
Start with the option that cannot hurt quality. Compress PDF re-saves the file with compact object streams and drops outdated object versions that pile up when a document is edited and saved many times. It never touches images or fonts, so pages look identical. It takes seconds and shows you the percentage change straight away.
Be realistic about what to expect: text-heavy files from older software and files saved many times often shrink noticeably, while scans and recent exports from office suites barely change, because their size is image data or they are already compact. If the result is not enough, move on.
Step 3: remove what the recipient doesn't need
Every page you leave out is size you don't have to compress. With Split PDF you can keep only the relevant pages – the signed pages of a contract, the chapter someone asked for, the statement for one month – and drop appendices, blank scan pages and duplicates. Type the pages to keep, for example 1-4, 9, and download the result.
Step 4: reduce image resolution
If images are the problem, they need to be stored with fewer pixels or stronger compression. This step is lossy, so keep your original. Choose the resolution for the way the document will be used:
| How the recipient will use it | Sensible image resolution |
|---|---|
| Reading on screen | 100–150 DPI |
| Printing text documents at home or in an office | 150–200 DPI |
| Printing photos or fine detail | 300 DPI |
The best place to do this is where the PDF was created:
- Word: Save As → PDF → "Minimum size (publishing online)".
- LibreOffice: File → Export as PDF, then enable "Reduce image resolution" and lower the JPEG quality.
- Scanner apps: scan text documents at 200 DPI in grayscale instead of 300–600 DPI in color. A 600 DPI color scan contains nine times the pixels of a 200 DPI scan, each with three color channels instead of one.
If you only have the PDF, a desktop tool can re-encode its images. Ghostscript is free and widely used: gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -o smaller.pdf original.pdf targets about 150 DPI images (/screen goes down to about 72 DPI). On a Mac, Preview's File → Export with the "Reduce File Size" Quartz filter works in one click, but it often makes images very blurry.
For scanned documents there is also a do-it-yourself route with PDF Hut: convert the pages with PDF to JPG at 1x or 2x in JPEG format, then combine the images with JPG to PDF. The result is made of pictures only, so use it for scans – never for documents with real, searchable text, which would lose that text layer.
Step 5: split into several emails
When a document is still too large, send it in parts. Use Split PDF to cut it into sections that each fit – for example pages 1-40 and 41-80 – and name them clearly, such as contract-part-1-of-2.pdf. Mention in the message how many parts to expect, so the recipient knows when they have everything.
Step 6: send a link instead
For very large files, a download link beats any compression. Google Drive, OneDrive, Dropbox and iCloud's Mail Drop can all share big files, and Gmail and Outlook offer to do this automatically when an attachment is too big. Before you share a link to a confidential document, check who can open it, whether it expires, and whether you need to remove access afterwards. Our guide on handling sensitive PDFs covers what to consider.
A quick checklist
- Find out the recipient's limit, or aim for under 10 MB.
- Check size per page to see whether text or images dominate.
- Try a lossless re-save with Compress PDF.
- Remove pages the recipient does not need.
- Re-export or re-scan with lower image resolution.
- Split into numbered parts, or share a link.
One warning: if the PDF carries a digital signature, any of these steps invalidates it, because the signature covers the exact bytes of the file. Send signed documents unchanged – by link if necessary – and do all compression before signing.