The attachment control has these limitations:
-
Attachments are supported with SharePoint lists and Common Data Service entities.
-
Upload and delete functionality only work inside a form. Attachment control will look disabled when in Edit mode and not inside a form. Note that in order to save the file additions and deletions to the back end, the end user must save the form.
-
You can only upload files up to 10 MB in size.More information:control-attachments
2.Yes. You can set with if function.
You can set the submit icon's visible as :
You can set other conditions if your want on your side.
More information:
Hope this could be helpful.
Best Regards.
Yumia