PDF-XChange Editor

What works

• smooth natural scrolling on magic trackpad and magic mouse! not silk smooth, some stuttering, but close to apple native scrolling and usable (pixel-level scroll, with inertia).
• annotations - rectangles, lines, underlines, strikeout, highlights with custom fill color.
• save, incremental save

What does not

• crash - a very large pdf e.g. a 400+ pages book, try search using Find... or Search... command or scrolling through all these pages, consume too much memory, more than it's native counterpart, also consume memory without return to it's operating system which crash the process. This is not rare use case for me, seriously reading and annotating will also crash the app because of this same memory issue likes every 15 minutes.

Workarounds

What was not tested

• Any of the extensions related to the PRO version.
• printing
• signature
• DRM
• OCR
• this is multi-feature app, not sure if I miss something. 

Hardware tested

Graphics:

• GPU:
• Driver:

Additional Comments

To date I can't find any other PDF apps better than this one, most of others are way too much streamlined (take away the real useful little feature), poorly-optimized, poor user interaction, opensource PDF annotation is still premature, this PDF-XChange one is the most well done PDF application in both features and usability.