If you paste the text anywhere else (like Notepad), does Word still crash?

Also, Microsoft Word uses non-standard "Microsoft" coding, which often does not convert well when pasted test from Word into non-Microsoft programs. Microsoft does this intentionally to discourage use of non-Microsoft programs. This can also be causing the issue you are seeing.

Or it is just a Windows and Word problem, in which case, you need Microsoft help.

'Notepad works just fine. Word and Thunderbird were the interaction issues, but I resolved it. The new Windows 10 Creative update (this last week) caused changes to how clipboard handles large amounts of text - ie, cut, copy, and paste. And it was another program (Malware-bytes) that didn't like it. So, when I tried to paste all that clipboard text to Thunderbird, Malware-bytes was viewing the collusion in a negative light and trying to scan the activity, which caused office/word to crash. The solution was to upgrade to the newest beta version of Malware-bytes where the situation is solved. So many apps - so many interactions. Just glad I got it solved.