I have a black shape like this:
That red rectangle is not part of my shape. I just draw it so that divides my shape visually into two parts. I would like to only scale “the part of my shape inside red rectangle” horizontally (I do not want to scale “the part of the shape outside rectangle” horizontally). How can I do this in illustrator?
Since you are asking about Illustrator — Grab the Direct Selection Tool (the White arrow) and click the anchor points on the left, and move them. That’s all there is to it.