This conversion seems to represent transformation of FontoForge Spline font databases (.sfd) to an OpenType font file (.otf). It appears that you can perform this sfd to otf conversion with several dedicated font converters, including FreeFont Converter or the Online Font Converter.
Convert Fontforge Spline Font database file format to OpenType font file format.
We have found 2 software records in our database eligible for .sfd to .otf file format conversion.
On-line services software - convert sfd to otf on web
A free web service for font conversion
Convert from sfd file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned sfd to otf. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A tool for online conversion of fonts