I have a question about this circuit.

Is 0.6 voltage drop od D1 enough to comepnsating forward voltage drop on D2 ?
I don't think so because there are another two resistors R1 and R2 which produce voltage drop ?

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i think...

R3 limits the current through D1 to stop a short circuit to ground, but enough to keep a 0.6 volt drop across D1.

R1 then limits the current from "in" to ground also preventing a short circuit to ground.

You'll find the voltage out will indeed be compensated, however if you draw too much current it will falter.

 

It depends upon the current.

It's a lot better than nothing.

 

That circuit looks like it is designed for a small RF signal. D1 and D2 should be matched and thermally linked for best performance.
If you want a "perfect diode" for relatively low frequency signals then the OpAmp rectifier works well:
Simple Precision Rectifier

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I agree. It looks like an envelope detector for an AM modulated RF or IF signal to recover the modulation (amplitude variations).

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Carl