The days of downloading PDFs to view them are over. With PDF Viewer Pro you can easily see all PDFs in your current conversation in the side bar. PDFs can open in a window so you can see them without downloading them or leaving the agent view. If you'd like, you can also open them in a new tab. Finally, a download button is also offered for situations where you need to store the PDF on your computer.
Click Install. Please check to ensure you don't have "Require authentication to download attachments" enabled. For more details see the Zendesk help page here: https://support.zendesk.com/hc/en-us/articles/203927716-Attachments-in-Zendesk-Support#sec5