Manuscripts for scientific peer-review are delivered as PDF files. Thus it appears most natural to comment the PDF file itself instead of submitting the comments as a separate text (file).
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf Allowed PDFSETTINGS are /screen, /ebook, /printer, /prepress, /default. (from the ghostscript package)gs -sOutputFile=output.pdf -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dAutoRotatePages=/None -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH input.pdf (from the ghostscript package)