you need part files also to open assembly file. for your problem you need 4 catpart and 1 catproduct. and collect them into same folder.
1/ if you have the .CATPart files this isn't a problem
* you can go File->Desk -> and then select the any element -> (contextuel manu go for) Find-> and then .... you know the rest!!
2/ if you don't have the CATPart Files you can not solve the problem!!