First, open your mobile web browser (e.g. Google Chrome)
Type wa.me// in the address bar and enter your phone number with your country code E.g., if your WhatsApp number is 9989XXXXXX, then write wa.me//+919989XXXXXX
Now a page gets displayed with the option of "Continue to chat". Tap on it
Now you will reach WhatsApp directly, where your own number will be displayed
Here you can send text, photos, videos, or files just like any other regular chat
You can also Pin this chat, so next time you have to note something, you can write in this chat
With this WhatsApp trick, no one other than you will see this message