Open Word → File → Options → Trust Center → Add-ins. Check "Require Application Add-ins to be signed by Trusted Publisher." Add the Design Science certificate manually.
The software provides a toolbar with over 500 specialized symbols , including support for matrices, multiline equations, and chemical notation via the integrated ChemType toolbar. mathtype 6.9b
Why cling to an old version? The math equation market has fragmented. Here is the comparison: Open Word → File → Options → Trust Center → Add-ins
If you have a valid legacy license key, installing MathType 6.9b is like finding a vintage Swiss watch—precision engineering from a bygone era. If you are a new user without a license, do not pirate it. Instead, decide: subscribe to MathType 7, learn native LaTeX (Overleaf), or use the free, open-source EqTeX or LibreOffice Equation Editor for basic needs. Why cling to an old version