Circuit Studio reads Altium SchDoc (schematic) files, libraries and project files just fine.
The current version doesn't read/write Altium PcbDoc's, in favor of it's own format, but I hear "rumours" the next release will read/write PcbDoc's.
Be advised the current version of Circuit Studio does not have an integral Gerber Viewer/Editor, but there are a lot of free/inexpensive ones out there. Viewmate seems to be a nice one for free, or $99 depending on desired features.