Hi, If your project is an enterprise project, ie it was created using an Enterprise Calendar within Project Server, then you will need to modify this calendar (and this is done by the Project Server administrator).
However, you say you are using a local copy – if this is an .MPP plan and it is not stored on the server, then you should be able to modify the Project Calendar – Tools – Change Working Time, and set the exceptions for the holidays you require. Tasks will now be rescheduled.
I’m guessing your issue here is – “I tried to add these non-working days to the custom calendar but I’m not able to change that.” – I don’t really understand what custom calendar you are trying to change – you should be changing the Standar (Project Calendar)
