Use Arduino Uno digital pins instead of ESP8266 I would like to know if this is possible.

I am using an ESP8266-ESP01, which only has 2 digital pins. I have a project that needs 3 digital pins so I have planned to use my Arduino, so I can use more digital pins. My plan is instead of plugging the sensor in the GPIO1 of the ESP8266, I could somehow plug it in the Arduino digital pins and the data would just be transferred to the ESP8266 and be uploaded to an online cloud.

I can read the sensor data in the Arduino but I don't know how to transfer the data to the ESP8266 so the wifi module would just receive it and send it to the online cloud.

If anyone can help me to get some idea specifically on sending the data from Arduino to the ESP and receiving the data from the Arduino.

Thank you.
DDA's answer is perfectly correct.
Like he says you need to check the voltage and use a logic level shifter.

However looking at it from another angle there are a whole range of ESP that have an increasing number of digital pins.  You could look at using an ESP-5, or an ESP-12E, these have different forms and increasing number of digital pins.

You could also look at the Wemos range, I believe there is an UNO form board and there is the Wemos D1-Mini, which has 10 digital and 1 analog.

Running on two boards is usually more of an issue than running on one board, god help you if you have synchronisation issues!