Outlook 365 treating pdf attachment as malware

[Malware-Outlook]

On an attached .pdf file for simple expenses that were combined, we keep getting the following error when sending the .pdf file Outlook 365. The recipient doesn't receive the pdf and Microsoft Exchange keeps rejecting this pdf. We renamed it to something simple like 1.pdf and even took out any highlights, tried reducing and optimizing, but the issue remains that we are not able to send the attachment. 

Error Message:

This message was created automatically by mail delivery software. Your email message was not delivered as is to the intended recipients because malware was detected in one or more attachments included with it. All attachments were deleted. Ran the pdf through VirusTool and came up empty. 

How can I tell if there is some type of malware embedded and how do I remove it? I have removed all text from the enclosed pdf file, but if you send it as an attachment, MS Outlook/Exchange 365 will flag it as malware.

Thank you!

[Abambo]

Hi @Malware-Outlook!

How did you create the PDF file? Until now, I did not see any Adobe program involved. And PDF files can be created by multiple non-Adobe applications.

I would ask this question in a forum for your mail delivery software. You could also try using an external mailing service like Gmail for testing. Just to circumvent a possibly ill configured mailing software.