For very old versions of Lightroom or Photoshop to support newer cameras Adobe recommends to convert native, proprietary RAW files to DNG format.
Snippet from an Adobe support page
What if I own an older version of Photoshop or Lightroom?
You do not have to buy a new version of Photoshop or Lightroom just to
get the latest camera support.
Adobe provides backwards compatibility for the latest cameras for free
in Photoshop CS, CS2, CS3, CS4, CS5, and CS6 as well as Lightroom 1,
2, 3, 4, and 5, through the Adobe DNG Converter. With this tool, you
can easily convert camera-specific raw files from supported cameras to
a more universal DNG raw file.
Another snippet explaining need of DNG format -
Why is DNG necessary for legacy version support?
The difficulty with supporting Adobe Camera Raw plug-in updates for
legacy versions of Photoshop and Lightroom is that camera
manufacturers are creating new proprietary raw formats each time they
come out with a new camera—and new cameras are coming out faster and
in greater volume.
It’s untenable to keep updating previous versions of the Adobe Camera
Raw plug-in and support new cameras/raw formats in a timely fashion.
Using the DNG converter is the fastest way to deliver backwards
compatibility to all customers (CS1–CS6; Lightroom 1–5; Photoshop
Elements 3–13; as well as third-party apps that support DNG).
Put simply, the DNG Converter allows Adobe to support the most
possible customers and cameras.
You can download the DNG convertor tool from this link - Adobe Digital Negative Converter