How do I use digital pin on sensor to analog on arduino uno I am working on a autonomous fire extinguisher.i have run out of pins.I have the following question in my mind while working on my project

Is it necessary that the DO pin in a flame sensor must be in a PWM digital pin in Arduino.i have this doubt since when I connected it to non PWM pin it didn't worked.

Secondly it is possible for me to use the analog pin in Arduino for the DO pin of the flame sensor or trigger/echo pins of the ultrasonic sensor.

Thanks.
PWM stands for Puls Width Modulation and is only available when the Digital Pin is in OUTPUT mode.

And YES, you can connect the flame sensor's D0 to any digital pin on the Arduino.

And yes it is possible to connect the flame sensor's D0 to a analog pin, but why not use the A0 from the flame sensor and connect it toi a analog pin on the Arduino?