Conclusions :

1. I tested with AN10 and ADC work perfectly with HPWM. Also, works well with AN0 and AN1.(another ADC I not tested)
2. ADC on AN6 pin work perfectly if I config APFCON1.3 = 1 and manually set for CCP.
3. I think that all troubles was from PIC revision...may be I'm wrong
4. I'll modify my PCB and I'll use AN10 ( this pin is near AN6)
5. In my opinion , is the best if avoid to use PORTC.2 (AN6) .
6. I prefer to work with HPWM because I can set very easy the freq and duty cycle .

Thank you again to Richard and Alain for your help!