iMessage shows a red exclamation mark next to your PDF. 'Not Delivered.' Or the upload stalls indefinitely.
What's actually going wrong
iMessage allows up to 100MB attachments but reliability degrades on weak cellular signals. SMS fallback (for green-bubble recipients) caps at 1-3MB depending on carrier. And recipient devices on older iOS may struggle with large attachments.
For consistent delivery, keep PDFs under 20MB.
The quick fix
Compress the PDF. Most files drop to under 5MB. iMessage delivers instantly, SMS fallback works if needed.
For scanned documents (often the size offenders), compression frequently brings 50MB+ scans down to under 5MB.
If that didn't work
If the recipient is on SMS (green bubble), iMessage's larger limits don't apply — your phone falls back to MMS which has very small limits (1-3MB). Either compress more aggressively, or share via AirDrop, email, or a cloud link.
For PDFs above 20MB even compressed, share via iCloud link. Mac and iPhone both support 'send as iCloud link' for oversized attachments.
Prevent it next time
Compress before sending. Know whether recipients are on iMessage (blue) or SMS (green) — the limits differ massively. And use iCloud links for large files.
FAQ
What's iMessage's exact attachment limit?
Officially 100MB. Practical reliability degrades on cellular above 20MB. SMS fallback (green-bubble recipients) caps at 1-3MB.
Does iMessage compress PDFs automatically?
No, PDFs send as-is. Images get compression options; PDFs don't.
Can I send a PDF via iMessage on Mac?
Yes, same Messages app on Mac sends PDFs to iMessage and SMS contacts. Drag the PDF into the chat or use the attach button.
Why does my iMessage PDF fail to deliver?
Either size (try compression), weak cellular signal (try wifi), or recipient device issue. Compressed under 5MB rarely fails.
iMessage PDFs send reliably under 20MB. Compress in Flint and ship.