Because of what, when saving an illustration as PDF, it turns into a blot?

Question

Adobe Illustrator

I use Sketch App.
I'm trying to save the illustration in PDF, but the result is a gag (I'm attaching a screenshot).
Why is this happening, and how can this problem be solved?

Answer 1

The difference between vector graphics and raster graphics.
expert-polygraphy.com/vektor_i_rastr/
rasterize the vector and save