Keeping a record of blade profile is a really great idea! Whether you sharpen your own, or take it to a skate tech, it can be useful to know how the shape changes.
I like to place the blade portion on the edge of a photocopier (or printer with a scanner built in), and photocopy it... Be very careful not to scratch the glass. After you are done, lay the blade against the copy to make sure the scanner didn't distort the image. This captures the entire blade shape, and may even see the name of the blade. If the toe pick teeth aren't symmetric, photocopy both sides, so you can see the shape when flat against the paper of all the teeth. (The relationship of the rocker portion of the blade to the toe pick is very important. E.g., blades feel a lot different when you don't have to roll forward as much from the sweet spot to the first toe pick as you used to.)
But I have also tried tracing the blade with a pen or pencil. Again, on the edge, so the blade is flat against the paper, like the other two said.
Any time you trace something, you have to be careful to keep the pen or pencil vertical, so it's wobble doesn't affect the line drawn. You also want the point that rests against the blade as thin as possible, to reduce shape distortion. technical pen works well.
technical pens like this you can buy in art supply stores or eBay for $2-$4 are great. Pick a good brand like Koh-I-Noor Rapidograph, or Faber-Castell. That's far more expensive than the 10/$1 pens I usually get at dollar stores, but they produce very thin consistent lines, darker, better and more symmetric than a typical ball point pen or sharpened pencil, and have very thin points. Maybe that is why engineers and artists like them...
BTW: Most good skate techs, including some mail order places, do an initial sharpening in which the skate tech modifies the shape to match what they think it should be. Especially with MK and Wilson blades, which are ground a bit inconsistently. (Ultima tend to be more consistent, IMO.) That's good, because it helps get rid of manufacturing defects. It's also bad, because the effective blade shape associated with a given blade model differs from one skate tech to another. But, we can only do the best we can.
Don't be surprised if your left and right blade have a little bit different shape. But that's not intentional, unless your skate tech has customized the blade shapes for your needs, something very few skate techs would ever do.