Text that is pasted into the editor from e.g. a website, word, pages m.m. usually gets the wrong font that is preset on the page.
The reason for this is that you also copy with a code for the formatting that is not visible to the eye.
To get past the problem, you can copy the text into e.g. notes in the computer first.
Then all hidden formats will disappear when you then copy the text from notes further into the editor.
In the editor, there are also two functions you can use if you do not use notes before.
Under Edit in the menu, there is "Paste as text" and if you have pasted the text before, you can also use "Format" under Format in the menu.