Blocking pdf showing in the Attachment Viewer Preview?

[hm_stella]

Hi folks,

I am currently working on the instant application - attachment viewer to share the output.

Each polygon feature creates the output, and I would like to save them as attachments to share with the public easily. The problem is that the output format is pdf.

When I built an attachment viewer and took a look to see if things worked well, the PDFs were shown in the viewer. That is okay, but I want the public to click the link and download it like the zip file does. 

Is there any way to show the pdf file as the attachment link?

Thanks!