I like to annotate papers I read in a digital way. Numerous programs exist to help in this process. For example, on OS X one can use programs such as Skim or even Preview. However, making annotations is dreadful when one wishes to add mathematical annotations, such as formulas or greek letters. A cumbersome "solution" is to select the desired symbol one by one using the Special Characters palette, though this considerably slows down the annotation process.

Is there any way to add mathematical annotations to a PDF? The only two limitations that I would impose on a solution is that 1) the mathematical text needs to be selectable, i.e. it must be text and 2) I want to limit the number of programs I need to make the process as painless as possible.

Some of the more promising solutions I have tried include generating LaTeX with LaTeXiT, but it seems to be impossible to add a PDF on top of another PDF. Another attempt was to use jsMath to generate the symbols and copy-paste these as annotation using one of the jsMath fonts. This results in unreadable, incorrect characters.