Pdf compression returns invalid file

I am currently evaluating the compression REST apis.  I am getting results via the GET request where the compressed file is returned however I am getting errors stating the returned file is invalid, I am correctly extracting the returned file from the returned string and converting it to  Uint8Array or even Arraybuffer but neither yields a valid file and I am extracting just from the %PDF string in the returned data and I have tried compressing different files - all yield same results