Open the Google Drive file you want to embed.
Click on the "Share" button in the top-right corner of the screen.
Click on the "Advanced" link in the bottom-right corner of the "Share" dialog.
In the "Who has access" section, set the visibility options to "On - Public on the web".
Click on the "Save changes" button.
Click on the "Copy link" button in the "Link sharing" section to copy the URL of the file.
<iframe src="https://drive.google.com/file/d/YOUR_FILE_ID/preview" width="640" height="480"></iframe>