How to make a PDF smaller for email
If a PDF is too big to attach, you have two options: make it smaller with Compress PDF, or split it into several files that each fit under the limit. This guide shows both, with a measured example.
Worked example: a 34.8 MB inventory report
In this test we used a fictional nine-page check-in inventory from Northfield Lettings: a contents page and eight pages with one room photo each. The file was 34,758,564 bytes, about 34.8 MB, which is too big for most email accounts.
With the Balanced preset, Compress PDF produced a file of 14,246,426 bytes, a saving of 59.0%. The Smaller images preset reached 13,192,167 bytes and High image quality reached 22,937,612 bytes. When we entered a target size of 20 MB instead, the tool tried its highest quality setting first, found it too large, and stopped at the second setting with the same 14.2 MB result.
The image list explained why the saving was not bigger: five photos were reduced, but three were left unchanged because the file went over the tool's pixel budget for one pass. Running Compress PDF again on the downloaded copy reduced those three as well, and the file came down to 1,913,741 bytes. The five photos already reduced were left as they were on the second pass.
We also split the original file with Split PDF and a maximum size of 10 MiB. That produced a ZIP with four PDFs of 3, 2, 2 and 2 pages, each between 8.65 and 8.72 MB. These are the results for this one test file; your savings depend on what is in your PDF.
Check the attachment limit first
Find out the limit before you start, because it decides how small the file needs to be. Google says the limit for personal Gmail accounts is 25 MB, and that a Google Workspace administrator sets the limits for work and school accounts. If the attachments are too big, Gmail adds a Google Drive link instead of attaching the file.
Microsoft Support gives a 20 MB limit for Outlook.com and other internet email accounts in Outlook, and this includes the message as well as the attachment. For work accounts on Microsoft 365, Microsoft documents a default maximum message size of 35 MB for sending, which administrators can change to anything from 1 MB to 150 MB. Attachments are encoded when they are sent, which adds about a third to their size and counts towards that limit, so with the 35 MB default the largest attachment you can send is roughly 25 MB. Some older Microsoft pages give lower figures for business accounts, so ask your IT team if you are unsure.
The recipient's limit matters too, and it can be lower than yours. Aim comfortably below the smaller of the two. In the target size box, 1 MB means 1,048,576 bytes, so a target of 20 allows up to about 21 million bytes. Enter a lower figure if you want more headroom.
Compress the PDF with a preset
Start here. A preset is quick and you can compare the result before downloading anything.
- Open Compress PDF and select or drop your PDF. The limit is 100 MiB and 500 pages.
- Choose a Compression preset. Balanced uses 75% image quality and resizes photos to at most 2,048 pixels on the longest side. Smaller images uses 50% and 1,024 pixels. High image quality uses 85% and 4,096 pixels. Preserve image quality only rewrites the file structure.
- Select Measure and optimise. The dialog shows the original size, the download size and the saving.
- Open Image processing results to see which images were reduced and which were left unchanged, with the reason.
- Select Compare original and result and look at the smallest text and the most detailed picture.
- Select Download optimised PDF. If no saving was possible, the button downloads the unchanged original instead.
Compress to a target size
If you know the limit, type it into Target size in MB (optional). The button changes to Compress to target size. The tool then works down through six settings, from 85% quality at up to 4,096 pixels to 25% quality at up to 512 pixels, and stops at the first one that fits. That way you get the highest quality that meets the target.
If no setting fits, the tool says so and offers the smallest result it made. That usually means the PDF holds content the tool cannot reduce. Splitting the file is the next step.
Split a PDF by maximum file size
Splitting keeps every page at full quality and sends the document as several attachments. It also works for PDFs that compression cannot shrink.
- Open Split PDF and select the PDF. The export settings open with Separate PDFs in a ZIP chosen.
- Set Split method to Maximum PDF size.
- Enter the limit in Maximum PDF size (MiB). The default is 10. Use a figure below your email limit.
- Select Download ZIP. The parts are named part-0001.pdf, part-0002.pdf and so on, and each one is measured during export.
- Unzip the download and check the first and last page of each part before sending them, in order, in separate emails if needed.
Why some PDFs barely shrink
Compress PDF reduces photos and scans, whether they are stored as JPEG or in a lossless format. Screenshots and diagrams stored losslessly are only changed when that saves a useful amount, and a PDF that is mostly text is already small, so the saving may be close to nothing.
Large photos can also be skipped. One pass handles up to about 64 million pixels in total, and no single image over 16 million pixels. A 12-megapixel phone photo uses 12 million, so a PDF with many full-size photos may need a second pass. Run Compress PDF again on the downloaded copy and check the image list each time.
If one page is bigger than the split limit on its own, Split PDF stops and tells you which page. Compress that page, raise the limit, or send it another way.
Check the file before you send it
Open the downloaded file, not the preview. Check that every page is there, that small print and figures in photos are still readable, and that any parts are in the right order. Our guide to compressing a PDF without losing readability covers what to look for.
Compression does not remove hidden information such as author names, attachments or comments. If the file is going outside your organisation, read how to remove hidden data from a PDF before sending it. The work happens in your browser on your device and your files are not uploaded; you can check that nothing is uploaded yourself.
Related tools and guides
- Is it safe to upload PDFs to online converters?
- Compress PDF
- Split PDF
- Compress a PDF without losing readability
- How to remove hidden data from a PDF before sending it
- Combine and split PDFs in the right order