When you add a attachment to a doc, as you issue:
your doc: 101 has a attachment sample.pdf.
so when you check you 101 doc, you can get the following property:
"attachment_list": [
"sample.pdf"
],
then you can update 101 doc that remove attachment_list property or remove attachment from attachment_list.
then you can not access the attachment.
also I am not sure that the attachment is removed.
you can try.