This is the "graceful compromise." It allows the file to open, but inside a sandboxed window where Editing, Saving, Printing, and Macros are disabled.
If you have ever tried to open an old .xls file from 1998, received a corrupted .pptx , or watched a user panic because an email attachment opened as a wall of garbled text, you have witnessed File Block Settings in action. file block settings in the trust center
When Microsoft introduced the Open XML formats ( .docx , .xlsx , .pptx ) in 2007, they fixed structural security, but billions of legacy files remained in the wild. This is the "graceful compromise