Help Editing A Font With the Pencil Tool Adobe Illustrator

On the desktop version you can set up the pencil tool to edit selected paths. I don't remeber if the setting exists on the iPad.

As Bobby said: use the Pathfinder functions on the iPad. Be careful: they only create groups. If you are done with it, you have to convert it to a path incase you want to send it to a plotter.

Drawing over the top of a letter shape will only create a new object stacked on top of that letter shape. Editing vector-based objects is very different from drawing on a pixel-based canvas, such as a document in Photoshop.

Tools like the Direct Selection tool and the Pen Tool can modify the path of an existing vector object, such as a letter shape from a font. Pathfinder tools can be used to weld two or more shapes together, or use one shape to cut through another one. Many methods can be used to modify vector objects.