Is it possible to add and display a .PDF file to an HTML email?
This question has more to do with the capabilities of the email client (such as Outlook or Mozilla Thunderbird), than it does with the Chilkat API (or any API).
If a particular email client is capable of inline displaying a PDF (and I don't know if any have this capability), then it's just a matter of constructing an email having the same MIME structure. Perhaps inline-displaying a PDF in email will be common in the future. If so, then it's simply a matter of viewing the MIME source of the email to see how it's constructed, and then use the Chilkat API to construct the same. Most likely, it would be to simply add the PDF as a file attachment in the normal/standard way, and the email client would automatically display it. (Again... I'm not saying email clients can display a PDF inline, because I haven't yet seen it. But if they can, then this would be the solution.)