An Outlook user had a problem when pasting into Outlook items:
I can't find an option in Outlook that will enable me to change the paste values to keep the original formatting.
After pasting into an email message, you should be able to click on the Paste Options button at the end of the pasted text and choose from paste options to merge formatting, keep formatting, or paste as plain text. (Keyboarders can press Ctrl key to expand the Paste Options button.)
If you don't see the little Paste Options button that lets you change the format after you pasted the text, go to File, Options, Mail and click on the Editor options button then Advanced. Near the bottom are paste options. The Show Paste Options button when content is pasted option needs to be checked. You can also set a default paste type for several different scenarios from this options page.
I like to compose e-mails in Word and then copy and paste into the body of an Outlook e-mail. When I paste it into Outlook, it uses Calibri, not the font I used in Word. It used to use the Word font. What changed?
It sounds like the paste options were changed. Change the paste options to use source formatting. You may also want to show the Paste Options button so you can easily select from the various paste options.