The description of how LATEX<#497#><#497#> font attributes are turned into TEX<#498#><#498#>
fonts is usually kept in a font definition (|.fd|) file. The
|.fd| file for family <#500#>family<#500#> in encoding <#501#>encoding<#501#> is called
|;SPMlt;ENC;SPMgt;;SPMlt;family;SPMgt;.fd|, for example |OT1cmr.fd| for Computer Modern Roman
or |T1ptm.fd| for Adobe Times.
Whenever LATEX<#502#><#502#> encounters an encoding/family combination that it
does not know (e.g.~if the document designer says
|<#503#>ptm<#503#>|) then LATEX<#504#><#504#> attempts to load the
appropriate |.fd| file. ``Not known'' means: there was no
| | declaration issued for this encoding/family
combination.
The declarations in the |.fd| file are responsible for telling
LATEX<#505#><#505#> how to load fonts for that encoding/family combination. If
the |.fd| file could not be found, a warning is issued and font
substitutions are made.