CRDOWNLOAD is a temporary file extension used by the Chrome web browser. Files with this extension are called Chrome Partial Download files, so seeing one means that the file isn't completely downloaded.
Partial downloads are due to the fact that either the file is still being downloaded by Chrome or that the download process was interrupted and so it's only a partial, incomplete file.
If the CRDOWNLOAD file extension is being used because Chrome is actively downloading something, it will usually automatically remove the ".crdownload" portion once the download finishes.
A CRDOWNLOAD file is created in this format: <filename>.<extension>.crdownload, or sometimes <Unconfirmed><#>.crdownload. For example, if you're downloading an MP3, it may read something like soundfile.mp3.crdownload or Unconfirmed 1433.crdownload.
How to Open a CRDOWNLOAD File
CRDOWNLOAD files are not opened in a program because they're really just a byproduct of Google's Chrome web browser — something that is produced by but not actually used by the browser.
However, if a file download in Chrome has been interrupted and the download has stopped, it might be possible to still use a part of the file by renaming the download. This can be done by removing "CRDOWNLOAD" from the file name.
For example, if a file has stopped downloading, say one called soundfile.mp3.crdownload, part of the audio file could still be playable if you just rename it to soundfile.mp3.
Depending on how long the file will take to download (like if you're currently downloading a large video file), you can actually open the CRDOWNLOAD file in the program that will eventually be used to open the file, even though the whole thing isn't yet saved to your computer.
As an example, say you're downloading an AVI file. You can use the VLC media player to open the CRDOWNLOAD file regardless of whether it has just started downloading, is halfway finished, or is nearly complete. VLC, in this example, will play whatever part of the file that is currently downloaded, meaning you can begin watching a video only moments after you've started downloading it, and the video will continue to play so long as Chrome continues to download the file.
This setup is essentially feeding the video stream directly into VLC. However, since VLC doesn't recognize CRDOWNLOAD files as a common video or audio file, you have to drag and drop the CRDOWNLOAD into the open VLC program in order for this to work.
How to Convert a CRDOWNLOAD File
CRDOWNLOAD files are not yet in their final form, so they can't be converted to another format. It doesn't matter if you're downloading document, music file, video, etc. — if the whole file isn't there, and therefore the CRDOWNLOAD extension is appended to the end, there's no use in trying to convert the incomplete file.
However, keep in mind what you learned above about changing the file extension to that of the file you're downloading. Once you have the file saved with the proper file extension, you might be able to use a free file converter to convert it to a different format.
For instance, if that MP3 file that only partially downloaded, is usable in some form, then you might be able to plug it into an audio file converter to save it to a new format. However, if this is to work, you need to rename the *.MP3.CRDOWNLOAD file to *.MP3 (if it's an MP3 file you're dealing with).
More Information on CRDOWNLOAD Files
When a normal download takes place in Chrome, the browser attaches this .CRDOWNLOAD file extension to the filename and then usually automatically removes it when the download finishes. This means you shouldn't ever have to manually remove the extension unless, of course, you're trying to save part of the file like what's described above.
You won't see Chrome append .CRDOWNLOAD to the end of a file during the download unless you're viewing the file in the folder where it's being saved. In other words, Chrome itself does not show .CRDOWNLOAD at the bottom of the screen during a download; it shows the true file name and extension (e.g., ubuntu.iso, not ubunto.iso.crdownload).
The size of a CRDOWNLOAD file grows as more of the file is downloaded. For example, if you're downloading a large, 10 GB video, you'll notice that at the very start, it's just a megabyte or two, and then as more time passes and more of the file is saved by Chrome, the size of the file will increase up to 10 GB when it's finished downloading.
Trying to delete a CRDOWNLOAD file may prompt you with a File In Use message that says something like "The action can't be completed because this file is open in Google Chrome." This means the file is locked because it's still being downloaded by Chrome. Fixing this is as simple as canceling the download in Chrome (so long as you don't want to finish the download).
If every file you download has the .CRDOWNLOAD file extension and none of them seem to be downloading completely, it could mean that there's an issue or bug with your specific version of Chrome. It's best to make sure the browser is completely updated by downloading the newest version from Google's website.