Compress a PDF to Send It as an Email Attachment
When a PDF won't send, you may have hit an attachment cap: Gmail allows 25MB total per email, Outlook and Microsoft 365 about 20MB, and most others land between 10MB and 25MB. An oversized message may bounce or become a cloud link. To try reducing the PDF, add it to Compress PDF, set a target below the cap, review the per-file method, and click 'Compress files'. Processing is local, with nothing uploaded. Check the result size before attaching it. Below: the real limits and how to work within them.
What are the attachment limits for each provider?
The cap applies to the whole message — every attachment plus the body — not to a single file, so packing several PDFs into one email is the fastest way to blow past it. Size against your recipient's provider, not just your own, since the smaller of the two wins.
- Gmail: 25MB total per email; over that it auto-converts the file to a Google Drive link.
- Outlook / Microsoft 365: about 20MB on the web, and the desktop client is similar by default.
- Yahoo / iCloud Mail: roughly 25MB and 20MB respectively; larger files route through Mail Drop or a link.
- Rule of thumb: aim for ~80% of the cap — receiving gateways often enforce a stricter limit than the sender's.
How do you shrink an oversized PDF enough to send?
Check how far over the limit you are. A file slightly over may shrink enough, but results depend on its content and method. A much larger file, such as a 40MB scanned contract that must fit in 25MB, may need a different export or fewer pages.
- Open Compress PDF and drag in the file you want to send (add several at once if needed).
- Enter a target in KiB below your provider's byte cap and leave room for the message body. Check the displayed bytes and the actual output before attaching.
- Review each file's method, then click 'Compress files'. 'Keep selectable text' is the default; 'Compress as images' loses selectable text and may lose detail. Check output bytes before sending.
- Compare before/after, confirm it's still legible, download, and attach.
Sending several PDFs at once and going over?
Because the cap is per message, three or four files stack up fast. Two ways out: compress each one smaller, or combine them into one file and compress that.
- Compress each separately: give each a share of the cap — four files under a 20MB cap means ~4–5MB each.
- Merge then compress: use Merge PDF to combine them into one, then compress the result under the cap — one download, nothing missed.
- If it still won't fit: trim with Delete Pages, or use Split PDF to send across a couple of emails rather than forcing it.
- Skip the 'large attachment' link when you can: for anything formal, a real attachment under the cap beats making the recipient click through to download.
Frequently asked questions
Gmail says my attachment is over 25MB — how do I send the actual file, not a link?
Compress the PDF under 25MB (aim for 20MB to leave headroom) and it sends as a real attachment instead of being converted to a Google Drive link. Compression runs locally in your browser, with nothing uploaded.
I need to email several PDFs and together they're over the limit — now what?
The cap is the message total. Compress each file smaller, or use Merge PDF to combine them into one and compress that under the cap. If it still won't fit, trim pages with Delete Pages or split across a couple of emails.
Will compressing make it unreadable for the recipient?
It can if you choose 'Compress as images', which may soften small print and detail. Start with 'Keep selectable text' and check every page. A target does not guarantee readability or that the email will be accepted.
Are my email attachments uploaded to compress cat's servers?
No. Compression runs in your browser via WebAssembly, so the PDF you're sending stays on your device and never touches a server.
Updated · compress cat team