Customers can't open my PDF's

Good Afternoon.

Recently, more and more of my customers can't open the PDF's I sent them. I believe I downloaded some 'addon' that is not present on the standard install and you cannot open or see the PDF without the recipient also having to download this addon. The problem comes that quite a few clients are not able to download anything on their computers as they have strict controls in place, such as councils and governments. I annotated a diagram I scanned in and I believe the software thought this may be another language and may have installed an eastern text font.

How can I see the installed font and how can I delete it?

Regards.