im going to purchase bootstrap studio . before that i wanna know that can i copy paste html and css from the saved files to dreamweaver or something like dat.
When you export your site you have all the files and you actually "have" to upload them to where you want them, so yes, that would be exactly what you can do. :)
On the other hand, unless you have something so horrendously complicated to add to your site, there should be no "need" to open the files in Dreamweaver or any other outside app. Do understand though that if you edit them in Dreamweaver or any other app, those changes are not importable to Bootstrap Studio, or in other words, the changes will not be there when you open your project again in BSS.
You would be better off looking at BSS as your all in one tool ... OR
Looking at BSS as your put it all together tool so that I can edit it from then on in Dreamweaver or my favorite text/html editor.
Unlike some tools that have proprietary files (files that are specific only to that specific app), although BSS is like that as well, you can create Custom Code blocks to add things that you want to be in your project that you have either added to your page(s), or that you were experimenting with outside of BSS. This gives you the freedom to use your favorite text/html editor to experiment with things until you have it working and then add it to your project once you do. Somtimes it will need to be a Custom Code box and sometimes it won't. Depends on the type of element you want to add.
BSS is pretty versatile though, there isn't a whole lot that you cannot do with it other than editing PHP and a few other high end languages at this time.