AFAIK exit code 6 is Error. Whats your instdir?
May you have to specify output dir
code:
Section "SaveAsPdf"
DetailPrint "Installing SaveAsPdfAndXps Extension"
SetOutPath $temp
File 'Prereq\SaveAsPDFandXPS.exe'
ExecWait '$TEMP\SaveAsPDFandXPS.exe' $0
DetailPrint "SaveAsPDFandXPS exit code = $0"
Delete '$TEMP\SaveAsPDFandXPS.exe'
SectionEnd