Currently Adobe Camera RAW does not yet support the Sony RX100 RAW files, so you will need another program to open and process the files. If you do not yet have one I recommend the Sony Data Image Converter ver 4.1, which is quite a small program and can be downloaded for free here
I personally just use it to open the RAW files and re-save it as TIFF files so that I can open them in Adobe Camera Raw.
CAUTION: When opening the files in the Sony Data Image Converter, I highly recommend that you go to the Noise Reduction option and turn it OFF. The noise reduction algorithm in the program is pretty bad and will leave the images looking like water color paintings. Initially I was really disappointed with the quality of the RX100 images, but then when I turned off the noise reduction...Wow...the differences was night and day. If you want to apply noise reduction I suggest you do it in Adobe Camera Raw, you will get much much better results.