save forecasted data

roberto_rematchemie,

I think you are missing the purpose of Project's baseline. When you set a baseline, several Project fields are saved in baseline fields. This provides a "baseline" (i.e. the original plan) for comparison to the current plan via earned value metrics and/or variance fields.

The current plan is updated (i.e. "real" start/finish, etc.) either in bulk via the Update Project feature or on a task by task basis using the Actual Start, Actual Finish, Actual Work, and Remaining Work fields. You should NOT be saving a new baseline as part of the update process. A new baseline should be set only when a change in scope is needed (e.g. tasks added/deleted).

So, you do NOT need to create a separate copy of the file as part of the update process but I do highly recommend periodically saving your file as a backup in case your file gets corrupted or other things that may cause a loss of data.