PDFill Tools has an easy user interface and merges, splits, extracts, watermarks, etc. and is free.
http://www.pdfill.com/pdf_tools_free.html
It needs, and also automatically installs, GhostScript (Lite).
When you install it, it also installs an evaluation copy of PDFill Editor which does all of the above and a whole lot more. But the evaluation copy puts an obnoxius watermark in the center of each page until you buy it. Don't know why they bother including it when the PDFill Tools software is free, does what you want, and does not add a watermark.