On Mac, you can drag and drop files into entry.
Once your file is attached, it can be edited. After making changes to the file Diarly will detect the change and send the new version to iCloud.
Please note that when making changes to the file on two devices at the same time, only the last version will be used.
On iOS, when writing or editing the text, an editor toolbar will be displayed where you can click on the icon. This will show you an option to attach Picture or File.
You can also share files from other apps, using the share extension. You can read more about sharing photos in Apple User Guides.