Inky is the new PDF reader on the block that supports ink annotations. Launched as Dink, and then renamed, Inky is a UWP app compatible with both Windows 10 and Windows 10 Mobile.
Still in beta, Inky is an app to read and modify PDF files that also supports annotations. With support for Windows Ink, you can not only use the pen for annotations on Windows 10 devices like the Surface, but you can also add annotations on Windows 10 Mobile devices with touch.
You can create notebooks and add PDFs to the same using drag and drop and share the documents with anyone from within the app.
Inky is free at the moment, although ad-supported. It works well for most parts, but the user experience could be more intuitive. It took me a while to understand what notebooks are and where are my files were getting saved. But it’s in beta, so hopefully things would get better. Download Inky from the Windows Store, and let us know how you like it.