long word doc stuck when searching on several computer but rename....

i got a very weird case. maybe someone knows the reason.
i have this 120 page word document containing telephone numbers and names i a table.
when you tried to search a string , word stoped responding almost every search.
i suspected the document was buggy so i moved it to another place on the network (win95 netbeui 12 users) and it didnt help.i gave up
one of the users just SHORTENED ITS NAME and VOILA! work like new.
i cant understand it do you?