Found in Microsoft Documentation:
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To archive project plans, follow these steps:
1. Create a new Project Server account that is named Archive. To do this,
follow these steps:
a. Log on to Project Web Access as an administrator.
b. Click Admin, click Manage users and groups, and then click Add User.
c. Click the Project Server authentication, using a logon name and password
option, and then type Archive in the User Account box. Complete all the
required fields, and then click Save Changes.
2. Create a new security category that is named Archive category. To do
this, follow these steps: a. In Project Web Access, click Admin, click
Manage security, and then click Add Category.
b. In the Name box, type Archive category.
c. In the Available users and groups box, click Archive, and then click Add.
d. In the Set Permissions with Template list, click Project Manager, and
then click Set Permissions with Template.
e. In the Projects: Select the projects that users in this category can
view section, click the Only the projects indicated below option, and then
list the plans that you want to archive.
Note If you want to see these project plans in Project Center, add views to
this category.
f. Click Save Changes.
3. Assign all the old plans to this project manager. To do this, follow
these steps: a. Open the plan by using the Archive account in Microsoft
Office Project Professional 2003.
b. Click Resources.
c. In the Resources pane, click Add columns of custom information.
d. In the Add columns pane, click Book Type, and then click Insert this
Field.
e. For all the resources, click Proposed in the Booking Type column. This
will remove the tasks from the user Timesheet views.
4. Republish the plan in Project Professional 2003. To do this, follow these
steps: a. Click Collaborate, point to Publish, and then click Republish
Assignments.
b. Clear all options except the Become the manager for these assignments
option.
c. Click OK, and then close the plan.
By following these steps, you will set up the category so that only the
Archive account can view the plan. This method will remove the project plans
from the Project Center views and from the Resource Center views. These plans
will continue to be reported in the OLAP cube.