This thread lists Windows 8 PDF annotation apps (Modern UI aka Metro UI) with pen / stylus support. __________________________________________ Recommended: Drawboard PDF, Drawboard ($10, trial available) - link Pen, freeform highlighter, word highlighter, stroke eraser, 40 pen colors, 20 line widths, undo/redo, radial menu, insert blank pages, create new PDF, insert shapes, insert image, insert camera snapshot. Annotation history pane. Autosave to protect against data loss. Tabbed document view. Regular app updates. Continuous scroll. Simultaneous pen and touch (no tool switch needed), option for drawing with finger/capacitive stylus. Pressure sensitive ink, currently as free add-on option, will likely become paid subscription add-on at some point. You can now leave feature suggestions on Drawboard's UserVoice page. MetaMoji Note ($12, free lite version) - link Excellent general note taking app, but can also be set as the default tool for PDF import and annotation. The description states that users can save as a new PDF, not sure if it can save back to the original PDF. Simultaneous pen and two-finger touch, but not pen plus single finger touch (touch also draws). Great sampling rate (smoooth ink). Radial menu with customizable pens. Lasso select, infinite (?) undo levels. Doesn't recognize hardware pen eraser. No continuous page view, but two finger swipe to next page works, and it offers a page thumbnail navigation bar that can stay on-screen, as well as a 'jump to page' button. Reader, Microsoft (free) - link One black pen with fixed width, yellow text highlight with cursor (tap text to show selection handles). Some issues: doesn't recognize transparent ink from PDF Annotator (and others?), sometimes loses annotations after app switching, blocky ink pre-rendering at high zoom levels. No pressure sensitivity. Standout feature: tabbed document view. Foxit Mobile PDF for Win8, Foxit (free) - link Eight pen colors, four transparency settings, four line widths. Manual switch between inking and panning mode. PDFNotes, Omtinez (free) - link App description states it's a beta for now. Notes are not readable outside app for now. Xodo Docs, Xodo (free) - link Offers ink, notes, text, signature, shapes. No distinction between pen and touch, and need to activate 'edit' mode to ink, and no panning while inking. Does not recognize the Surface Pro pen eraser. PDF Touch, Suneet Shah ($3) - link Highlight and ink, five pen colors, sliders for width and opacity. Manual switch between touch and ink, no saved custom pens. Annotate101, KL Software ($5, trial available) - link Mentions digitizer based annotation, haven't tried it yet. Perfect PDF, soft Xpansion ($2.50, trial available) - link Looks relatively full-featured, but tools are hard to get to. Example: supports pen markup under context > tools > ink + shapes > pencil. That's a long way to go for every new annotation. On my quick try it popped up a menu after every single pen stroke, which makes natural writing impossible. Bug? __________________________________________ Please use your own judgment working with these apps - I cannot vouch for their reliability or security. After trying any new app, please leave a review in the Windows Store so us 'serious inkers' are heard. If the apps above don't cut it, consider the following non-metro alternatives: PDF Annotator is a good option for those not on Windows RT. Customizable toolbars with multiple pressure sensitive pens, freeform highlighters, text markup tools, etc. Drawbacks: slow scrolling performance on Atom, you need to manually switch from ink to panning or pan by touching outside the page area (edit: fixed in version 5), and relatively expensive ($70, or $30 for students, free trial available). Panning is not very smooth on an Atom slate, but it works. PDF Revu 12 is a more expensive choice ($220/$110 educational, free trial available), but it's really very good in Win8. Touch panning and pen annotation without switching tools, relatively smooth panning, tons of options, pressure sensitive ink as well. Works surprisingly well on an Atom slate (trying this with Ativ 500T). No touch fling though on my system (page doesn't coast / immediately stops scrolling on release).