Cannot open .pdf file in an outgoing email message

I scanned a document from my printer (HP OfficeJet Pro 9018) into my iMac (OS 11.6.6) and saved it in Finder/Documents.  I can open it in that location.  When I copied it (drag and drop) from Finder/Documents into an email I was preparing, it would not open in the email location, meaning the email recipient will not be able to open it either.  Before sending the email, I tested opening it and instead of the file opening a message box opened stating:

The file “The Guard Episode #6 - 7/18.pdf” couldn’t be opened

because you don’t have permission to view it.

To view or change permissions, select the item in the Finder and

choose File > Get Info.

This is puzzling in that I have created many such files in the same way that I have attached to emails and the recipients have been able to open them.

My inquiry, therefore, is threefold. #1 Why won't this file open from the email? #2 What specific steps do I need to take make this file able to be opened by the email recipient?  #3 What specific steps do I need to take to prevent this from occurring with future scanned documents?