Suppose you have lost / corrupted your pdc primary domain controller how you can recover your dc how you can do that ?

You should have ADC in operatoin along with PDC if that is the case your ADC will take care the all domain level stuff however you need to do the following task to make things error free network.

1. Replace your PDC entries in with ADC so that all user can be contact ADC in the DNS settings.

2. Seize your FSMO roles from ADC and there after your ADC will become the PDC ultimately.

3. You can install new windows server and promote to DC.

4. At this stage either you can transfer FSMO roles back to new DC or leave as is with the old PDC.

Now both server up and running and you should not have any problem.

ADC will act as PDC in THE FAILURE OF pdc.

You should have a secondary DC specially if you have a larg network, to recover your DC if you dont have a Backup Solution then you may try Windows Bulitin System Restore.

seizing FSMO roles only in case no hope that PDC will not go live again complete dead . then we can seize if it will become online just matter of maintenance  the no need to seize roles .

sezing fsmo roles will force transfer fsmo roles from dead pdc to adc .

First take a cold backup of your ADC ... or convert it to virtual . then seize ur fsmo role by checking the DNS SOA records. After this install new windows on PDC & promote it to DC .

you have to creat BDC server after creat PDC. IF any thing happend with the PDC that time BDC work as PDC. After creating BDC it's synchronize all the data configuration with the PDC.

will seizing the FSMO roles work?  and playing wihtout back up is not safe :) ... have a look at the following tutorial .. 

http://support.microsoft.com/kb/255504

Practical question.

We need to sieze the role from Domain server.

in case we loose our PDC then our ADC will now act as PDC. 

you can recover the corrupted one and it will replicate with the ADC.

For any FSMO roles server failure, you need to seize your FSMO roles from any domain controller, this DC will become the PDC emulator role carrier.

you can transfer PDC Emulator to any ADC with seize  commands while you fix the primally PDC Emulater host