Make a prototype from an existing site

After a day of research and many tests, I need your help:

from an existing site (let's take for example stackoverflow.com) I would like to be able to create a prototype/model of a modification of this site

The goal is not to recode the modifications in HTML/CSS => I only need a prototype (in PPT, in adobe XD, in adobe PSD, or other) and I wish that the solution is not too heavy, I have to make prototypes on a hundred sites.

Do you have any tools or ideas to answer this need?

My tests for now:

• Convert the site to pdf then to ppt to make the modifications on PowerPoint => very bad quality of conversion/printing. In PDF, we lose the formatting of the site.
• Using a plugin on Adobe XD => quality a little less bad, but the design of the site is off too.

I'm not a great developer but if there is another method a little more technical, I'm interested.