Extension of the output mask will be used as

Defines how the extension of the output mask will be used:

as Replacement - to create a name of the output file the extension of the output mask replaces the extension of the input file. For example if the output mask is *.PRN and input file is FILE.PLT, then the resulting output file will be FILE.PRN.
as Attachment -  to create a name of the output file the extension of the output mask is attached to the name of the input file. For example if the output mask is *.PRN and input file is FILE.PLT, then the resulting output file will be FILE.PLT.PRN.