Highlighting a PDF that contains no fonts

I love the Acrobat's commenting tools. I especially enjoy the highlighter tool, with it's dozens of colors and ability to change opacity levels. Using Acrobat's highlighting tool, I have infinitely more control over colors than I do using traditional hardcopy highlighters. However, with Acrobat's highlighting tool, I've encountered a few problems that make it less than suitable for my highlighting needs:

• I can only highlight actual fonts, (as seen in the document Properties dialog box).

• In my daily workflow as a technical communicator, I also encounter scanned documents and CAD files, both of which typically contain no fonts. I can run OCR and then highlight the text, but often, the OCR is unpredictable, as Acrobat doesn't always go a great job of recognizing text blocks. (The following example shows how Acrobat skipped an entire paragraph of text.)

• Finally, there are times when I need to highlight circular objects, but alas, I cannot. So in order to highlight these documents, I have to print them out. I have tried using the rectangle tool and ellipse tools, but they obscure the text. Even when I add a fill color and reduce the opacity, the text and objects that I'm trying to make more obvious, in reality become more obscured.

So I got to thinking about what makes key behavior of the highlighter tool different than the rectangle tool. It has to do with how the comment's color interacts with the objects beneath it. Sounds like a blending mode to me… Multiply!

So Acrobat's comments are capable of interacting with the document using the multiply blending mode...but I needed a way to make my own comments that can use take advantage of blending modes. For that, I went to Custom Stamps.

Acrobat's canned stamps are very business-like: "Sign Here," "Approved," and so forth. But you can make your own custom stamps for whatever purpose you like. You can even harken back to the early days of stamps, back in (I think) Acrobat 5, when the out-of-the box stamps were wacky monster-face clip art. (I remember thinking, "Why would anyone want to use stamps? That's dumb.") But Adobe wised up and included stamps that business professionals would actually use.

So I went into Illustrator and make a plain yellow circle and set the blending mode to Multiply. Then I save the file and create a custom stamp in Acrobat. Then I took a deep breath and then clicked on top of some text. WOOHOO! The text shows through! (The truly geeky among you will surely understand my anticipation and excitement.)

While experimenting with my new stamps, I started playing. Clicking frantically (actually, just to see how many stamps I could put down in just a few seconds). If the stamps interact with the document using a blending mode, how would the stamps interact with other stamps that use a blending mode? They multiply, as expected. But what I also discovered was that by clicking and dragging, I can control the size of my stamp. So a single stamp can make the same shape in varying sizes. And no need to hold down Shift. The down-side to this, however, is that the proportions are locked. I cannot turn a circular stamp into an elliptical stamp, or a square stamp into a long thick rectangular stamp. Bummer.

But let's say you just need to colorize drawings (CAD files, for example) and need a way to color code different circles and match them up to a parts list. The colored circles are sure a good start, but let's see how much more useful we can make this! Just for fun, I also made a circle using a gradient. Isn't it beautiful?

So let's say I have a parts list on one page that I need to match up with the drawing later in the document. I made some corresponding rectangular stamps in order to stamp the parts list. But I need to keep flipping back and forth between the two of them (parts list and drawing), color coding them simultaneously. I can't keep track of dozens of numbers in my head, but fortunately, I don't have to. Acrobat will let me see both pages at once. Go to Window>Split.

Now, I can see both my parts list and my drawing, all in one window, without my desk being cluttered by excess papers, and without being limited to the five colors of highlighting markers I have in the cup on my desk.

It did take some time to create my stamps and get them set up in Acrobat, but once I did, keeping track of technical details on engineering drawings became much easier and more efficient. And those CAD files were never so beautiful to me as when they had been stamped with sunshine gradient circles.

And so ends another day in my quest to bring visual interest to boring technical documents around the world.

Edit: 9-13-918
If you need an easier way to create highlighting objects in your PDF, check out my article on Bluebeam Revu. It's an amazing program designed specifically to meet the needs of users in Architecture, Engineering, and Construction. The drawing tools in Revu have a "highlight" checkbox, enabling any shape to act as a highlighter.