If print as image did nothing then it isn't a problem with PDF files, Print as image converts the job into a series of sequential bitmaps.
Try switching drivers between PS and PCL
Where it is only pdf, it isn't likely the driver, more likely the files, I will assume they are being made in-house, so.
If you get slow prints try enabling/disabling Print as image
If it works better with that enabled, the file is clearly the issue, it should be flattened, it should have the fonts properly embedded, and if you are making them, you should be using PDF/X instead, as it will fix those problems for you.
It could also be a file size issue, you are overflowing the buffer, which happens mostly when people drag and drop content into the file and then create the PDF, which means while the pdf displays as 72 DPI (They all do) pictures in it can be anything, like a 22 MegaPixel goliath from a DSLR. In which case the printer has to do the conversion to whatever the output is (Typically about 300DPI). That takes a lot of power to do, more than a printer has. If you import the file into Indesign/Word etc instead of drag and drop, it negates this issue by formatting it properly during the design process.
Xerox 6027 is printing PDFs incredibly slow! It prints a page, thinks for 15 seconds, prints next page and so on. And it behaves like this only for PDFs(not for all PDFs but for most of them). I am running windows 10. I tried a lot of things, different laptops, USB connection, changed drivers, changed Adobe Reader, got best results with:
- Postscript driver(PCL 6 is worse)
- Ticked in Adobe Reader "Let printer determine colors"
- disabled advanced printing features
But still it has 15 seconds delay between printings. Can it be fixed?