I'm not sure this is an appropriate section to ask this.
I need one more 5V source and dont want to use outer source
Could I use digitalPin as 5V source pin? as digitalWrite(pinNum,HIGH); ?
please help me
Yes, you can use a pin to power a resistive load (lighting a LED is an example).
If.. the load draws <= 20mA, and if.. the load is happy with a small volt drop.
Splicing the wire coming from the 5volt pin might be easier.
Tell us more if you want exact answers.
For example, OptiLoader uses (has used) a digital pin to power the AVR chip being programmed. I subsequently decided that this wasn't a particularly good idea, ass Arduino boards got more complicated, and more likely to have other things connected, but it worked fine for putting bootloaders onto old-style Arduinos that didn't have much more than the AVR chip (Duemilanove, Diecimila, etc.)