Difference between Attach File and Upload File in SharePoint List
While trying to work on fields with type 'Publishing HTML' or 'Multiple Lines of Text' in a list you may notice two options 'Attach File' and 'Upload File'. Attach File will be used to add the attachment to List. Upload File is not used to add the attachment to the item in the list that you are working on. Instead it is used to upload file to document library. Knowing the difference between the two helps in adding the attachments.