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Whenever I am bringing in a part to assemble, I cannot select any feature other than planes to add constraints.
I can select and features form the parts already there in the assembly but not the part the just bought. The part is acting like a whole body
If right mouse click, if the dialog is set to MOVE COMPONENT or SELECT ASSEMBLY ITEM, creo will behave that way. I've accidentally gotten there. That's the only thing I can think of right off hand.
Check the Reference control settings for part which is not working, File > Prepare > Model Properties > Change Reference and backup > Check permission for reference creation or reference for placement.