The actual error depends on the Office version, but the fix is always the same: The IT admin must either unblock that file type globally, or the user must use a third-party tool to convert the file to a modern format. Look closely at the File Block Settings dialog. For each file type, there is a third option nested in the dropdown: "Open selected file types in Protected View" (instead of blocking them outright).
In modern Microsoft 365 Apps (Semi-Annual Enterprise Channel), that override is often removed. If you block a file type, it is blocked . The only way to open it is for an admin to change the Trust Center policy or temporarily move the file to a whitelisted location (which is not a real fix). The Migration Strategy: How to Phase Out Legacy Formats If you want to finally kill .doc in your organization, do not flip the "Hard Block" switch tomorrow. That is a riot waiting to happen. Use a 3-phase strategy: file block settings in the trust center
"Blocking save prevents users from creating dangerous files." Reality: It prevents them from creating legacy files. They can still create a dangerous .docm (macro-enabled document) unless you block that separately in Macro Settings. Final Verdict: Should You Tweak These Settings? For the home user: Leave them at their default (Microsoft's out-of-box settings). The defaults block only the truly ancient and dangerous formats (Excel 4.0, Word 2.0, etc.). Do not unblock them unless you absolutely trust the source. The actual error depends on the Office version,
This is the "graceful compromise." It allows the file to open, but inside a sandboxed window where Editing, Saving, Printing, and Macros are disabled. The Migration Strategy: How to Phase Out Legacy
You must customize these settings. The default settings are too permissive for regulated industries (Finance, Healthcare, Legal) and too restrictive for engineering firms that rely on legacy CAD-to-Excel exports.