Combine files and reduce file size don't work together

If I combine files and the tab says, "Binder", then I click 'file' and 'reduce file size' it tells me no further reduction is possible.  Then I save the file as somefilename.pdf.  I am then able to click 'file' and 'reduce file size' and it does it.  So this is a two-step process and the error message the first time is incorrect.