Cad files to attachments

Unless I am missing something, I haven’t been able to attach cad files to the attachments area. Overall I have found it hard to use certain features within design files because I feel like I am never able to paste images I need to or add files that I need to. For example, when I created my contract template, I couldn’t paste my logo into the document. In attachments, I couldn’t add cad files. In tasks, I can’t paste images.