I bought a camera as Canon EOS 5D Mark IV, but the raw documents conducted by the camera could not be processed by Lr v. 5.7.1 I currently use. I wonder which version of Lr can process the new raw documents.
The latest version of Lightroom 6 or Lightroom CC are the only versions that will open raw files from that camera. It will be necessary for you to either upgrade or use DNG converter 9.7 to create DNG copies that can be opened in Lightroom 5.
The 5D Mark IV was first supported in Lightroom 6.7. You'll never be able to open those Raw files in 5.7.1.
So you have a couple of options: