As O_G indicates, it's possible that the file size of the document exceeds the maximum permitted by your email system(s).
However it's also possible that you're trying to email something that doesn't exist. You've told us that you scanned a document but you've not told us the format which you've saved it in. If you're simply viewing the document within the program that you scanned it to (without saving it first), it doesn't exist as a Windows file but simply as data held in temporary memory.