I have a notes/drawing drawn with light and thin color pencil. How do I increase the thickness of the color pen or pencil handwriting or the drawing and make it heavy weight and bold? How do I make my handwriting look more like a picture? What do I do if I want to change the shape of my handwriting? For example, I have this picture, Image source: https://commons.wikimedia.org/wiki/File:Parsec.jpg
You can do it in GIMP (which is free and open source)
Open the image and do Filters > Distorts > Value Propagate. Set the mode to "More black (smaller value)", then set the slider values as shown below. Adjust the thickness as desired by moving the propagating rate slider. You can also increase the Lower Threshold slider if the result is a bit blurry.
Here's the split view so you can see before and after
Note: If you feel this has gone a little too dark, it's also possible to use Colors > Curves to lighten it back up again, just a touch.
Using Adobe Photoshop...
Filter > Other > Minimum... from the menu and adjust to your liking...
You can make specific selections in areas and run the filter to refine things in a more direct manner. There are a couple dashed lines on the left which get fairly lost in the above. (I may have lost them with too great a Levels adjustment) So deselecting those areas may be helpful. Or selecting them specifically for a greater filter value, before adjusting Levels may help.