We have about half a dozen of Dynamic PDF Forms. The problem happens with exactly one and only one PDF Form Template, and it is a Dynamic Form. All forms have large amount of javascript, and it only happens with only one of them.
Following is the error we get from Office 365 malware detection engine:
Delete message. Malware: JS/Jasobfus.A!ml;JS/Jasobfus.A!ml;JS/Jasobfus.A!ml;JS/Jasobfus.A!ml;JS/Jasobfus.A!ml File: FullForm_uspap-latest-off-v1.pdf

If I send the PDF as attachment from/to GMAIL account, there is no problem.
I performed test with several PDF Forms generated from the same template over the past year (I got them from the backup). In some cases, the attachment did go through after I open the PDF form in designer, and clear the "Save Options" and save as Dynamic PDF:

But after I repeated the test with the master template and several other files, I realized that clearing or setting the above options has no effect. Also, there is no difference if the template is blank or it has data imported.
As of now, I have two different versions of the Dynamic PDF Form that belong to the same master template and one of them was blocked by the malware engine, and the other was not blocked.
What I will do now is that I will compare the XML View of the both versions and try to figure out what is the difference that is causing the form to be identified as infected with malware.
If you have any feedback, please let me know.
Tarek