I use pdftocairo as the default renderer in CUPS to print to my HP LaserJet printer. It's the tool that better manages PDF documents with shading and transparency (common in beamer presentations and PDFs generated by cairo). Everything worked fine until I discovered some pages in documents were incorrectly printed.
I tried to print a PDF document (produced by pdfTeX) containing the Helvetica-Narrow fonts, and some lines of the document exhibited wrong character spacing. I tried to print the same document using Chrome and the text was printed with correct spacing so the printer wasn't the responsible.
After changing the default PDF->PS renderer I discovered the fault was in pdftocairo because any conversion with pdftops and pdf2gs resulted in correct character spacing on my screen. Changing the PS language level did not work. Also, this bug doesn't manifest when pdfTeX uses the URW base 35 fonts instead of the Adobe ones.
I am attaching a PDF document that can be converted with pdftocairo, pdftops and pdf2ps with pdftocairo being the only one that looks different at the narrow fonts.
Thank you for your bug report, that's probably an upstream bug and should be reported to them on https:/