Send mail Acrobat reader message download acrobat in my mail in Outlook

HI,

2 users in my brand send pdf with acrobat reader, since 2 weeks when she's click to send mail outlook open with the pdf in attachment but with a message  :

Please find attached the PDF. Download Adobe Acrobat Reader for free to view and comment on this PDF ...

How to disable this message when she's send mail with acrobat reader?

Thanks