Problems with PDF quality on Photoshop or Illustrator

I am trying to export a PDF containing mobile app screens through Photoshop, but the end result comes out to be quite pixelated. Viewing it on 75% zoom makes the text appear better, but the images get distorted. The same is happening with PDF exported from Illustrator. Is this an issue with the Adobe suite? If this is the case then what is the best software to export PDFs from?

Thanks, Mayank