This app is simply excellent for developing ideas, communicating them visually, and also making markups (red lines) to PDF / CAD DRAWINGS. I very much enjoy the ability to change the colors of the paper, and am very impressed by the scale tools and ability to set the scale of the ruler visually. It is a very interesting convergence between the precision of CAD and the looseness of sketching. Drawing with an apple pencil on an iPad pro with this software is a true pleasure for architects ... So why four stars? (Update: March 2016: layers can be moved at will - thanks & sorry I missed that before...) Otherwise> The major problem is the resolution of imported PDF files - why is this so low, especially on an iPadPro?? It should be possible to pull in PDFs as in vector format, or otherwise to choose a high resolution import solution. Further areas which could be improved to move to 5 stars: 1. It would be great if there was an easier way to make straight lines without only using the skeumorphic ruler every time. 2. We should be able to define new line types & create our own stencils 3. The drawing tools - with the Apple Pencil - are not as flexible and material as with other drawing software, such as with Apple Notes...perhaps it would be possible to use the engine from notes, to share the "feeling" of the pencil across software...? Notably, it seems that there is not recognition of angle when holding the Apple Pencil. This would be a great improvement, too...But then, it would really start to be perfect. Dangerously so...