Learn how Mail handles PDF files attached to email.
When you send or receive an email that has a PDF (Portable Document Format) file as an attachment, depending on the file's size, you may see its contents within the Mail message, or you may see a document icon.
If the PDF file contains two or more pages, Mail displays it as a document icon.
If the document is smaller, Mail displays the contents of the PDF file within the message window.
To change the way the PDF file is displayed in the current message window, Control-click the icon or visible portion of the PDF and choose "View in Place" or "View as Icon" as appropriate from the shortcut menu. Note that this only affects how you see the PDF in this message's window, it is not a permanent change.