Possible migration path PDF document

[orryw]

Hello there,
i created a PDF document that i uploaded to a web page for free download. The PDF was written with Word 2016 and converted into PDF and contains Text and graphics. Now i got this securty note that wont allow to mark my PDF as HTTPS secure:
"Styling master document from stylesheets defined in HTML Imports is deprecated, and is planned to be removed in M67, around May 2018. Please refer to https://goo.gl/EGXzpw for possible migration paths."

I hope you can help me, i have no coding knowledge at all and just came to this site because of the link. Thank you