Previously, I had been annotating PDFs on my Nexus 7 (2012) using ezPDF Reader Pro (by Unidocs) with good results. The most useful feature was the ability to highlight text in different colors. (This allowed me to color code parts of articles, e.g. yellow for general claims, blue for details about the study/article, green for things germane to my work, etc.)
I've started using a Windows 8 tablet (an Asus Transformer T100TA) and wanted a similar program. Many PDF readers support highlighting in Windows, but many (such as the free Adobe Reader) only allow yellow highlighting. Changing the color of the highlighting should be trivial, and I don't think this feature is worth the $119 for Adobe XI Pro.
Fortunately, this post on superuser led me to Okular. Part of the KDE suite, Okular is popular on Linux, but it does run on Windows. The installation is a little larger than some other programs because KDE provides a platform for many different programs, but one doesn't need to install all of them to use Okular. The tools for reviewing are accessed via F6 or the Tools menu, but the default set includes several useless (for me) tools and only a yellow highlighter. The aforementioned post, however, describes editing a tools.xml file to customize the offerings.
On Windows 8, tools.xml file is located in
C:\ProgramData\KDE\share\apps\okular along with a folder named pics that holds the icons used. (The folder is probably in a different location on other versions of Windows, but searching for tools.xml should turn up the location.) I've uploaded my tools.xml file and some quick icons I made in Paint that match the highlighting colors I use below; changing the colors/tools shouldn't be difficult if my exact setup doesn't work for you. (The color/properties of individual annotations can be changed by right-clicking.)
When annotating PDFs in Okular, all of the changes are automatically saved but not in the PDF file itself. It can be a little confusing to open a file, see the highlighting, and then to email it a colleague where the highlighting has disappeared. The original PDF file that was opened does not seem to be changed by Okular. To save the highlighting in the PDF file itself, choose File -> Save As... The new file will display the highlighting on in other PDF readers on other computers.
In short, with a tiny bit of work Okular is a great, free tool for reading and annotating PDFs on Windows 8 and is comfortable to use on a tablet.
Customized tools.xml and icons (70 KB; .zip) - unzip into the above folder to use