How do I batch convert a bunch of pngs or other images into a single PDF on Mavericks? I took a bunch of screenshots and I want to make them pages in a single PDF. Selecting all four in Preview and exporting to PDF only exports two (?), separately. The "Export to PDF" File menu function adds a strange white border around the screenshots (and orients the page as portrait). So I converted each to PDFs individually and then combined them manually. I tried the solutions here, but Mavericks' Preview doesn't appear to work that way anymore. What's the best, free, hopefully built-in way to automate this?
You can use the convert command if you install ImageMagick. ImageMagick isn't always a simple install, but if you install Xcode and Homebrew it should be fairly painless.

convert *.png foobar.pdf

http://www.imagemagick.org/script/convert.php