Resize pdf to poster

That does not work, as the page ratios are different. You can do it, however, you will either have borders or you will have cropped of areas. 

We had a similar issue with posters, that got printed, and I adjusted the background in such a way, that I could scale the file accordingly, without cutting in the usefull area. I did that however with InDesign, and did output the files at the sizes needed.