To download a PDF file, you can follow these steps:

1. Open a web browser: Launch any web browser on your device, such as Google Chrome, Mozilla Firefox, or Safari.

2. Search for the PDF file: Use a search engine like Google or Bing to search for the specific PDF file you want to download. For example, if you are looking for a PDF on demographic attributes, you can search for "demographic attributes PDF."

3. Find a reliable source: Look for a trusted website or platform that offers educational resources and PDF downloads. One such platform is EduRev, which provides a wide range of study materials for various subjects, including UPSC-related topics.

4. Access the PDF file: Once you have found a suitable source, navigate to the webpage containing the PDF file you want to download. Click on the link or button that is associated with the download option for the PDF.

5. Save the PDF file: After clicking on the download link, a dialog box will appear asking you to choose the location where you want to save the file. Select a preferred location on your device and click on the "Save" or "Download" button.

6. Wait for the download to complete: Depending on the file size and your internet connection speed, the download may take a few seconds or several minutes. You can monitor the progress of the download in your browser's download manager or status bar.

7. Open the downloaded PDF file: Once the download is complete, go to the location where you saved the PDF file on your device. Double-click on the file to open it using a PDF reader, such as Adobe Acrobat Reader or any other compatible software installed on your device.

By following these steps, you should be able to download a PDF file on your device. Remember to always use reliable sources and exercise caution while downloading files from the internet to ensure your device's security.