Yes, you can install any version of MS Office as long as it is compatible with Win 8 or Win 10 (assuming you upgraded). It is recommended that you insert a SD card for additional storage capacity since the Stream 11 only comes with 32GB of eMMC storage. I think it can support up to a 64GB SD card.
Did you purchase a used / refurbished HP Stream 11? If so then that is likely why you cannot activate MS Office. If you purchased it new, then see if you can exchange for a new one because a new HP Stream 11 is supposed to give you a 1 year license to use MS Office 365 for free.
If you just need to use an office suite, then you can try OpenOffice which is free to use. Only "basic" Excel files are compatible though. Excel files that have macros in them or VBA code are not compatible with OpenOffice.
https
/www.openoffice.org/