A marketing user would like to send out a new whitepaper to their prospects and...

 The recommended way to accomplish sending out a new whitepaper to prospects and tracking who opens the PDF is to upload the whitepaper PDF as a content file and link to it in the body of the email. A content file is a type of file that can be uploaded and stored in the Content Builder, which is a tool that allows marketers to create and manage content assets. A content file can be linked to in the body of an email, which allows prospects to access the file by clicking the link. By linking to a content file, marketers can also track who opens the PDF, as the link will generate a tracking code that records the open activity. Uploading the whitepaper PDF as a content block, attaching it to the email, or embedding it in the email are not recommended ways to accomplish sending out a new whitepaper to prospects and tracking who opens the PDF, as they either do not allow linking, do not allow tracking, or do not display properly. References: : Content Files