Why does a pdf attachment open, close, then open an email attachment?

[defaultmu642bkwuw7r]

When I attempt to open a .pdf attachment, which was created from an excel document, it opens for less than a second, then closes, and then pops up an email compose window.  What steps does the creator of the .pdf attachment need to take to resolve this issue?  

For context, I'm just the frustrated recipient of the email that the .pdf is attached to.  I want to be able to tell the creator of the .pdf what he/she needs to do so her/his .pdf attachment can be read.  I receive the .pdf attachment every month so I'm constantly reminded about the problem.  Any help from the community would be appreciated.

[Karl Heinz Kremer]

Without access to the PDF file in question, it's impossible to say why the file is doing that.

Does this happen when you open the attachment from within the email application? What happens when you save the file first and then open that saved copy? 

This is definitley not normal. I suspect that there is a document level JavaScript in the file that is doing something and as a side effect, you see the email compose window active.