We've been getting lots of questions from faculty about annotations here at UVM and find that that term covers lots of possibilities and variations. So, feel free to describe in more detail what you would like to do if the following is on the wrong track:
We've had the best results in text, highlighting, underlining, or circle/square-type annotating by simply using Preview (if one is Mac-centered) or Adobe Reader (on either Mac or Windows platforms). In this case "best" is defined as easy, familiar and free. However, while you can annotate the pdf with a variety of text options and, in the case of Adobe, with audio (or even video if you buy the not-free Professional version), you cannot annotate it with an image, no picture on top of your pdf file.
Once annotated you put it online by attaching it to a blog post where it becomes a link for people to click and download.
Here's a slightly different approach that may be of interest: Thinglink. This is an online app that allows you to upload an image and then annotate it with text, pictures, links or video. So, no highlighting or red circles or squiggles. Instead, what you see is a picture of your pdf file with some circles on it. Hovering over the circles displays text, images, links, etc. (Some caveats: there are free and not-free versions with different features. There is an upcoming video version that lets you annotate videos, i.e. place annotations on a video.)
Now, to be clear, this is an image annotator so it is not annotating a pdf file, but if you are not expecting people to download and use the pdf as a pdf but instead want them to see some text that started out as a pdf file and now has annotations on it, it might do the trick. You would have to export the pdf file as a jpg (you can do that in Mac Preview; for non-Macs use zamzar.com). Then upload the jpg to Thinglink, annotate it, and then have it generate a link. Here's a really raw example:
http://www.thinglink.com/scene/609860816400809984
Like the pdf attachment, you could put this link into your blog. Yes, people would have to click on it but they would not have to download the file - it would just appear in their browser as it does here.
- Hope