Why does my scanned document fail to deliver when sending it as a text message to multiple recipients using iPad?

Sending by [SMS] text...?

The clue here is in the name/description. Text literally means text characters - and not a "document". As such, a scanned document (e.g., a PDF file) cannot be sent "as plain text" over SMS messaging to Android and other non-Apple devices.

iMessage (supported by Apple devices) and other messaging services, such as email, are far more flexible in being able to handle many document types and attachments.

SMS (a.k.a. Short Message Service) messages, a cellular legacy messaging technology, are limited to 160 text characters; modern devices can transparently chain-multiple message-blocks into a seamless single message.

In summary, you cannot send a scanned "document" by SMS messaging.

To send a scanned document as text, try these steps:

1. Reduce File Size: Ensure the document isn't too large. Compress the PDF if needed.
2. Convert to Image: Save the scanned document as an image (JPEG or PNG) and send it.
3. Use iMessage: Ensure you're using iMessage if sending to other Apple devices.
4. Send via Email: If text messaging fails, try sending the document via email.

If issues persist, ensure your devices have the latest iOS updates.

This would be because you are not sending SMS text between your Apple devices using the Messages App - but are instead likely using Apple's proprietary iMessage service.

The Apple Messages App has the capability to use both services; if both are available, iOS/iPadOS will use iMessage in preference - this protocol being feature rich and more secure.