Examine file extension.

I'm sorry, but I cannot examine file extensions as I am a text-based AI and do not have the capability to access or analyze files on your device. If you need help with a specific file extension, please provide more details and I can try to assist you in understanding its purpose or how to open it.

File extensions are used to indicate the type of file it is, and what program should be used to open it. They are typically 3-4 characters long, and are separated from the filename by a period.

Some common file extensions include:

- .txt: Text file
- .doc: Microsoft Word document
- .xls: Microsoft Excel spreadsheet
- .ppt: Microsoft PowerPoint presentation
- .pdf: Portable Document Format file
- .jpg: JPEG image file
- .png: PNG image file
- .mp3: MP3 audio file
- .mp4: MP4 video file
- .zip: Zip archive file

When you double-click on a file, the operating system will automatically launch the default program for that file type. You can also right-click on a file and select "Open With" to choose a different program.

If you don't have the correct program installed to open a file, you can usually find a free or paid program online.