qpdf 2.3.1 includes a handful of minor improvements. The most significant change is a fix for a threading problem resulting from non-thread-safe use of a third-party library. There are also a few updates to the documentation to fix previous errors or omissions, a workaround to a (fixed) ghostscript bug that caused some test failures under certain conditions, and a tweak to improve compilation with MSVC 2010. This version of qpdf also tests clean on a 64-bit Windows build. (Older ones probably did too, but this is the first time I have been able to try.) I hope the next release will include Windows 64-bit binaries.