@Arthur-Alunts ,
The font you set in Notepad++ is just how the text is displayed in the entire Notepad++ application – and every text file you open. Font information is not saved inside text files. If having multiple fonts in your document is important to you, then you need to look for a “word processor”, not a text editor. Notepad++ is a text editor, not a word processor. (Word processors include the bundled-with-Windows MS Wordpad, or MS Office’s Word, or free ones like LibreOffice. But word processors are not the subject of this forum, so that’s as much as you’ll get about word processors here.)