You can use the Files feature available on web, desktop, and mobile, to upload files of any format to your account and attach them to notes. Files are end-to-end encrypted using the same technology powering the encryption of your notes.
You can also choose to upload a file directly to your account storage without attaching it directly to a note:
If you have a paid subscription, you can also use the Super note type to embed your attached files directly into your note! Just type "@" to bring up the autocomplete dropdown list, then begin typing in the name of the file you want to attach. Once you see the file in the dropdown list, select it to embed the file into your note.