Let me know if I picked up the right file
Let me know whether I picked up the right file
Could anyone tell me the differences between them?
Can we use ‘if’ and ‘whether’ in present, past, and future tenses as well?
'Whether' implies more than one alternative (e.g. 'whether the day is wet or fine') so the addition 'or not' is understood even if it isn't included. Most people would understand both your sentences in the same way, but, as H2ONaCl implies, the first one is literally asking for a reply only if you picked up the right file, the second asks for you to be told whether it was the right one or not.