intriguing, pasting rtf to write usually works on all systems.
i’m sorry to hear that not even write.exe worked for you.

please try one more quick thing, before you file an issue report at the link at the bottom of this post.
just to make sure that notepad++ is able to correctly export formatted content to your clipboard at all.

• close notepad++ if it is open

• download this pre-built portable notepad++ npp.7.6.3.bin.zip from >>> here <<<.
  (this is a portable, ready to go version for testing. it works completely isolated from, and independent to your current notepad++ installation and independent to all your plugins. it already includes nppexport, and helps to eliminate any problems caused by your current installation)

• extract npp.7.6.3.bin.zip onto your desktop and open the resulting folder npp.7.6.3.bin

• double click on notepad++.exe to run this

• open any of the files you have tried before, select any part of it, and try to use plugins > nppexport > copy rtf to clipboard again.
  note: there should not be any error messages at the right bottom of the screen, or anywhere else, while doing this

• paste it to write.exe

if pasting rtf to write does not work now, there’s a possibility that some problems of your windows installation is causing this behaviour.

if you want to file an issue report, or contact one of the plugin’s developers, please visit this address:
https://github.com/chcg/NPP_ExportPlugin/issues

please keep us informed about any success or failure.
especially as i have not been able to reproduce this behaviour on windows 10 pro x64 and windows 7 pro x64 using nppexport to rtf/html and pasting to ms word 2010-2016

i assume that office 2016 as used in office 365 for business should accept rtf data from the clipboard, unless any recent windows update has removed this feature.

please try the following to make sure:

to make sure the clipboard gets correct rtf data from notepad++, we’ll make a ms write test:

• mark a segment of your document
• go to the menu plugins > nppexport > copy rtf to clipboard
• press the windows (start) button at the bottom left of your screen, and enter write.exe
  (write.exe is available on windows 10, windows 7, windows xp, and many others)
• double click on the write.exe in the search result list (above the write.exe you have just typed)
• paste your rtf clipboard content to write.exe

now if rtf pasting works in write.exe, we know that your ms word would not accept rtf and we have to use another format.

then you can try to use html content:

• go to plugins > nppexport > copy html to clipboard and try pasting this into word.

note: you can not paste rtf or html clipboard contents to the web version (online internet browser version) of word correctly.

if you are using the NppExport plugin:
first you have to mark a segment of your document (or press ctrl+a to select all)
then go to the menu plugins > nppexport > copy rtf to clipboard and then paste it for example to a new ms word document.