Hi @edogan0671 ,
Advance Steel can only use TrueType (TT) text fonts, defined in TTF files (example: isocpeur.ttf) in descriptions in drawing styles. ISO.SHX is compiled symbol file, not a TrueType text font.
What is an SHX file?
An .SHX file is an Autodesk AutoCAD SHape index file used to edit drawings in Autodesk software programs such as AutoCAD and AutodeskCivil with non-compilable SHAPE files. These files contain type information about SHP primitives and are essential for two applications: they are used to display the original indexing for a drawing and as a resource for SHX text files.
Contents of an SHX file
SHX files store the index information for custom DMesh as well as TrueType or SHP fonts, including Darkhorse, Dbarrow, and Deltablob. Arrows, lines, text characters, polylines, circles and arcs are all in the files. Furthermore, SHX files can also include advantageous additional values such as the fill attributes of the shapes.
Definition from dimension style manager - only TrueType text fonts available:

Otherwise, it is in dimension styles, where you can use all available fonts.
HTH
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