If Mark has a read-write permission to the share \fileserver\securefiles and a read-only permission to the file coolstuff.docx on the NTFS file system shared by the file share, he is able to perform the following actions:
Read the contents of coolstuff.docx.
Copy coolstuff.docx to another location on the file share or to another location on his local machine.
Create, edit, and delete other files and folders on the \fileserver\securefiles share.
Modify the permissions on coolstuff.docx or other files and folders on the \fileserver\securefiles share.
However, Mark would not be able to modify the contents of coolstuff.docx, as he only has read-only permission to that file