Among various that there are, I find one of the best and affordable Foxit PDF Editor. Very light, almost like Foxit Reader, ideal to make observations to a document that does not have the basis or responsibility, as is the case of working with the publishing house that is using Adobe In Design CS for Mac, and only generate the pdf.
Practically recognizes any object, image, figure and in the case of texts, group them in horizontal lines separating styles at the time of selection.
In this case, I want to make observations in an external word document with detailed explanations, what I do then is only to change to another color the content that must be edited or to make indicative figures.
In addition, it has interesting tools for this purpose, such as grouping segments, ungrouping and then selecting the segment you can change the color, size, import source, etc.
Images and figures
New images can be added, replaced or inserted. Both images and objects can be rotated in 90 degree sequences. Even the text. Basic shapes include rectangles, ellipses, lines, polylines, curves, and objects with gradient tones.
Once the changes have been made, the save button stores the changes. In case of not having a paid license, a mark is created in a corner that says that it has been edited with Foxit PDF Editor.
Not bad, it is to download it, test it and make sure that it is needed and then buy it. Among the most interesting functions is that you can import pages from another document indicating the page range and where we want to insert it.
Here you can download Foxit PDF Editor, on the same page you can see other solutions from the same company, including a development kit (SDK) and one in which you can make forms in pdf.