Remove Formatting When Copy/Pasting Into FileMaker Field

Under the field file > manage settings:

Choose field choose "Options"

Choose "Auto-Enter"

Check and Select and "Calculated value"

Press "Specify" and enter "TextFormatRemove ( Self )"

Uncheck the "Do not replace existing value of field (if any)"

Close and save.

You're all done. Formatting will be removed from pasting.