Most users don't know that Solidworks, which is well know as a mid level solution for CAD, is actually owned by the French company developing CATIA, which is practically used by every single serious manufacturer in the world (from automotive to aircraft to ship to factory to you name it).
The geometric kernel powering these two is now the same, but it wasn't for years. I guess it's a good illustration of why this acquisition was successful and didn't ruin Solidworks: the company was left practically untouched for more than ten years. "assimilation" took place at a very slow pace (almost cosmological for a software company).
Now the question to ask is more why the acquisition is taking place. To get a list of customers? To get skilled contributors, or knowledge, or patent, or a piece of technology? To get a presence in a different country? All or a part of this? To kill a competitor?
Anyway you put it, acquisition is not a neutral move. It's always joining a bigger structure, hence jumping to a later stage and size at extreme speed. Considering how difficult it is for a single company to get through its different stages by itself, it is normal that acquisitions are hard for acquired companies. Assuming the objective is not to kill the acquired, tremendous efforts will be needed on both sides to make it work. The acquiring company ramping up newcomers, on new actual processes, on new ways of doing; the acquired one to agree to it, and accept that it is the cost to pay to operate at a higher scale.