For most of the file types on your system, when you right click a file in Windows Explorer, you will locate the "Print" command.

Executing the Print shell command, will result in the file being sent to the default printer. For some file types, like .TXT, a hosting application (Notepad, by default) will open the file first, for some the file would simply be printed (Word Docuemnt - .DOC). Some file types do not have an associated print command application.

File - Right Click - Print. Who will print?

If your want to programmatically print files from Delphi code, using the associated shell application, you need to first make sure that there is an application associated with the shell's print command for a given file type.
uses registry;// get the application (+command line usage) assiciated with // the Shell PRINT command for a given file GetShellPrintAssociatedCommand(const fileName: string): string; var   extension : string;   extDescriptor : string; begin   result := '';   extension := ExtractFileExt(fileName) ;  with TRegistry.Create do   try     RootKey := HKEY_CLASSES_ROOT;     if OpenKeyReadOnly(extension) then     begin       extDescriptor := ReadString('') ;       CloseKey;     end;    if extDescriptor <> '' then     begin       if OpenKeyReadOnly(extDescriptor + '\Shell\Print\Command') then       begin         result:= ReadString('') ;       end     end;   finally     Free;   end; end;
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