Where CR2 files come from
CR2 is the RAW format used by many Canon EOS cameras, from entry-level DSLRs to professional bodies. More recent Canon cameras, including the mirrorless EOS R series, use CR3 instead. Both keep the sensor data so you can edit the photo later with a lot of flexibility.
The problem shows up when you try to use those files outside of photo software. Double-clicking a CR2 on a computer without the right codec may show nothing, phones usually can't preview them, and websites, print shops and messaging apps tend to reject them. If you set your camera to RAW only, you may have a card full of photos that nobody else can open.
What you get from the conversion
Canon cameras store a JPEG preview inside each CR2 and CR3 file, processed with the Picture Style you had set on the camera. ConvertirDocs takes that preview and saves it as a JPG. It's quick, it doesn't need Canon's software, and the colors match what you saw on the camera's screen.
To be clear about the limits: the RAW data itself is not developed. You can't recover blown highlights or change the white balance here. For that, use a RAW editor such as Canon's Digital Photo Professional or another program you prefer. The size of the JPG depends on the preview your camera stored: on many models it's full size, on others it's smaller.
Typical situations
You shot a birthday, a graduation or a football match in RAW and the family wants the pictures today. You're a hobbyist who wants to post a few shots on Instagram from a laptop with no editing software. You're a photographer sending low-effort proofs to a client so they can pick favorites before you edit. Or you just need one picture for a form that only accepts JPG.
In every case the original CR2 files stay exactly as they were. You download new JPG copies and keep the RAW files for serious editing.
If you shoot RAW+JPEG on your Canon, you already have JPG copies on the card. This page helps when you only kept the RAW files, or when the JPG copies were deleted to save space.
Nothing to install, nothing uploaded
The conversion runs in your browser. Your Canon files aren't sent to a server, which also saves you from waiting for big RAW files to upload. There's no account and no limit on the number of files: select a whole shoot and download everything in one ZIP.