.MS12 File

The ms12 file extension is associated with the NI Multisim, a SPICE simulation environment for Microsoft Windows operating system developed by National Instruments Corporation.

It seems that .ms12 file stores circuit design made using version 12 of the program.

Files with ms12 extensions  can be typically found as circuit board designs from NI Multisim version 12.

How to open:

Use NI Multisim version 12 and higher to open and work with .ms12 files.

How to convert:

Some sort of export to an exchange format is likely and can be done with the original tool.