Using New Outlook on Windows for personal email, calendar, and contact management
You use New Outlook, right?
If so, click on the Settings icon on upper right. then go to Accounts > Signatures.
The Edit signature box will come up.
You will then click on the "Insert" tab, you need to make sure you click on the edit box first, otherwise the Pictures icon will be grayed out and not clickable.
Then you click on the Pictures icon and it will give you option to find the file to insert.
Once inserted, you can drag it to resize it, add texts, And give the signature a name and save it.