When working with a document that has an attachment section, there is a couple of ways files can be added to those sections. One is to select Attach file, the user is able to choose more than one file at a time. The other is to drag and drop one or more files directly from a local folder to the upload area.
Is there a limit to the type of file?
There is an upper limit of 100MB per attachment file. Otherwise, there are no limitations on file attachments.