Continue working on a webpart that has been deployed

Question

I might not understand the whole concept of SharePoint yet, but is it possible to continue working on a deployed web part without the original Visual Studio-project?

We have a third party company that has built some web parts to our SP-site. Can we continue working on these web parts using whatever has been deployed to us in the WSP, or do we actually need the original project/code?

Answer 1

You need to request source code if you want to change the Web Parts business logic.

WSPs are sufficient if you just want to deploy their Web Parts (and not necessarily changing their business logic) between different SharePoint Farms.