import of content from html coded file into multiple widgets

I tried several approaches I found in the internet - but I did not succeed.
To add one time a kind of link/import in every widget would make it easy to actualize the content in just the one html coded file.
Any suggestion how to do?
For sure: better would be a widget manager, that links one master widget to all widgets of the subsites - but I did not find an actual plugin doing this (multisite network!).
Thank you,
Walter