Quick answer
Compress the PDF by downsampling its images: 150 dpi keeps documents readable on screen and usually cuts image-heavy files by half or more. Aim for about 70% of your email provider's limit, because attachments grow during sending. If one file is still too big, split it into parts or share a download link.
Most PDFs that bounce back from an email server aren't big because of the text. A 40-page contract written in a word processor is often well under 1 MB. The files that break attachment limits are the ones full of images: scanned paperwork, photo-heavy reports, slide decks exported to PDF, brochures made in design software. The good news is that images are also where most of the savings are, and you can usually cut them down a lot without anyone noticing.
This guide explains what actually makes a PDF heavy, what the common email limits are, what the different compression levels do to your file, and what to do when compression alone isn't enough.
Why PDF files get so big
A PDF is a container. The size depends on what's inside it, and a few things account for almost all of it.
- Images at print resolution. A photo taken on a phone can be 12 megapixels or more. Placed in a document, it often keeps that full resolution even when it only fills a third of a page. Print shops want around 300 dots per inch (dpi); a screen needs far less.
- Scanned pages. A scanner doesn't capture text, it captures a picture of the page. At 600 dpi in full color, a single letter-size page is a large image, and a 30-page scan is 30 of them.
- Embedded fonts. To look the same everywhere, a PDF can carry its fonts inside it. Usually only the characters that are used are included (a "subset"), but some exporters embed entire font families. Fonts with large character sets, such as Chinese, Japanese or Korean fonts, are especially heavy.
- Leftovers from editing. Some editors save changes by appending them to the end of the file, so older versions of pages and images can linger inside. Design apps can also embed an editable copy of the original artwork alongside the printable version.
- Duplicated resources. When PDFs are merged, the same logo or font can end up stored several times.
You can't see any of this from the page itself, which is why two PDFs that look alike can differ in size by a factor of 50.
Email attachment limits, and why a 24 MB file can still bounce
Every email provider caps the size of a message. These are the limits for the most common personal accounts:
| Email service | Attachment limit per message | What happens with larger files |
|---|---|---|
| Gmail | 25 MB | Offers to send a Google Drive link instead |
| Outlook.com | 20 MB | Offers to share the file through OneDrive |
| Yahoo Mail | 25 MB | Suggests sharing through cloud storage |
| iCloud Mail | 20 MB | Mail Drop can send large files as a link |
| Work email (Microsoft 365, Google Workspace and others) | Set by your organization | Ask your IT team; the receiving server may be stricter |
Two details catch people out. First, attachments are converted to text for sending (Base64 encoding), which makes them roughly a third larger, and many servers count that encoded size. Second, the recipient's server has its own limit, and it may be lower than yours. A practical rule: aim for about 70% of the limit. For Gmail that means keeping the PDF around 18 MB or less; for a 20 MB limit, around 14 MB.
What compression levels actually do
When a PDF tool "compresses" a file, most of the work is image downsampling: lowering the resolution of each image to a target number of dots per inch, then re-saving it as a JPEG. Fonts are reduced to the characters actually used and unused data is dropped, but images are where the megabytes go.
MyPDFDone's Compress PDF offers three levels. Here is what each one does:
| Level | Image resolution | Best for | Trade-off |
|---|---|---|---|
| Strong | about 72 dpi | Reading on a phone or laptop, previews, very strict limits | Small print in scans and fine details in photos get soft; poor for printing |
| Recommended | about 150 dpi | Most email and upload forms; everyday documents and scans | Barely noticeable on screen; fine for ordinary office printing |
| Light | about 300 dpi | Files that will be printed, fine print, drawings, signatures and stamps | Smaller savings, especially on documents that were already lean |
A useful mental model: resolution affects file size roughly with the square. Halving the dpi from 300 to 150 leaves about a quarter of the pixels, so image-heavy files often shrink dramatically at the Recommended level. Documents that are mostly typed text shrink much less, because there were few images to begin with.
Step by step: compress a PDF with MyPDFDone
- 01Check the size and the limitNote the PDF's current size and your email provider's attachment limit. Plan to land at roughly 70% of that limit to leave room for encoding.
- 02Upload the PDF to Compress PDFOpen MyPDFDone's Compress PDF tool and drop your file on the upload box. Files up to 100 MB are accepted.
- 03Pick a compression levelStart with Recommended (images at about 150 dpi). Use Strong only for on-screen reading, and Light when the file will be printed.
- 04Check the new size and the previewMyPDFDone shows the compressed size and a preview for free. Zoom into small print and photos to make sure they are still clear.
- 05Download and attachIf the result looks right, download it for $2.99 (paid once) and attach it to your email. If it is still too large, split it or send a link.
Uploading, compressing and previewing are free. You only pay if you download, and it's a one-time $2.99, not a trial that turns into a subscription. If the file can't be made smaller, MyPDFDone says it's already optimized instead of handing you a bigger file.
When compression isn't enough
Sometimes even the Strong level leaves a file above the limit, usually a very long scan or a catalog with hundreds of photos. You have three good options.
Split the PDF into parts
Break the document into two or three files and send them in separate emails, labeled "Part 1 of 3" and so on. With Split PDF you can cut by page ranges (for example, pages 1–20 and 21–40) or into equal chunks. Splitting at natural boundaries, like chapters or separate forms, makes the parts easier for the recipient to handle.
Send a link instead of an attachment
Cloud storage links have no practical size limit. Upload the PDF to the storage service you already use, set the sharing permission (anyone with the link, or specific people), and paste the link into your email. This is also the better choice for files you'll update, since the recipient always gets the latest version. For sensitive documents, share with named people rather than "anyone with the link."
Fix the source instead of the PDF
If you created the PDF yourself, re-exporting it can beat any compression. In most word processors and presentation apps, the export dialog has an option to reduce image resolution or optimize for the web; choose it before exporting. Cropping large photos before inserting them also helps, since cropped-out areas are often still stored in the file.
Tips for scanned documents
Scans are the most common reason a PDF is too big to email, and a few habits at the scanner make a bigger difference than any tool afterward.
- Scan text at 200–300 dpi, not 600. 300 dpi is plenty for text, even for printing. 600 dpi quadruples the data compared with 300 and rarely helps.
- Use grayscale or black-and-white for text pages. Color triples the raw data per pixel. Keep color only for pages that need it, like photos or colored stamps.
- Avoid photographing documents under uneven light. Shadows and gradients look like image detail to a compressor, so they take up space. A flat, evenly lit scan compresses much better.
- Compress once, from the original. Every round of JPEG compression loses a bit more detail. If you need a smaller version later, go back to the original scan rather than re-compressing a compressed copy.
- Check signatures and stamps after compressing. They are the details most likely to degrade. Zoom in on the preview; if they look rough, step up one level.
A quick checklist before you hit send
- The PDF is at about 70% of the email limit or less.
- You zoomed into the smallest text and the photos in the preview, and they're clear.
- Signatures, stamps and handwritten notes are still legible.
- Page count and order are unchanged.
- The file name tells the recipient what it is (for example, "Lease-2026-signed.pdf").
- If you split the file, each part says "Part 1 of 3" and so on, and nothing is missing.
If you are sending a signed contract or form, you may also want to read how to sign a PDF online, which covers what makes a signature hold up and how to keep a signed file from being altered.
Frequently asked questions
Gmail lets you send attachments totaling up to 25 MB per message. Larger files are offered as a Google Drive link instead. Because attachments are encoded for sending, a PDF somewhat under 25 MB can still be refused, so aim for about 18 MB or less.
Real text in a PDF is stored as font outlines, not pixels, so compression doesn't blur it. What changes is images, including scanned pages, which are images of text. That is why scans need a gentler level than documents with typed text.
Start with Recommended, which keeps images at about 150 dpi. That is readable on screen and fine for most printing of ordinary text. Use Light if the scan has fine print, signatures or stamps that must stay crisp.
Some PDFs are already optimized: mostly text, subset fonts and small images. There is little left to remove. MyPDFDone tells you when the file is already optimized and never hands back a larger file than you uploaded.
Usually only a little. The contents of a PDF are already compressed internally, so a ZIP archive rarely saves more than a few percent. Downsampling images is what makes the real difference.
Check how the service handles files. MyPDFDone transfers files over HTTPS, stores them privately and deletes them automatically 2 hours after upload. Nobody opens your documents, and they are not used to train anything.