The general process isn't too crazy. But, you may be in for a lot of work if you want to take the old Vanilla ACAD stuff and make it 100% ACADE-compatible. It all depends on how far down the rabbit hole you want to go.
First, create a smart title block. There are good walkthroughs in HELP, also check out Doug McAlexander's website. Incorporate this into a template. I keep a separate template for schematics, one for panel layouts, and one for pneumatics. It would be best to use a template size that is the same or very close to what exists in the vanilla drawings.
Once you have a template, start a new project in the Project Manager. Then, create a new blank drawing using your template. Save it in the project folder. That drawing will likely need some sort of configuration in the drawing settings - these will sort of depend on how your company does things. After that, you can bring in the vanilla stuff. Normally, I would recommend that you use the 'copy circuit' function but it won't matter here because nothing that you're copying is carrying any intelligence yet. (But once you're working within an actual ACADE drawing, you should stop using vanilla commands. Only use the ones offered by ACADE or you could break intelligence somewhere.) So, anyway, copy that stuff over, it really doesn't matter how, and then go back to the Project Manager. There, you will right-click on your project and select 'Add Current Drawing'. You'll be asked if you want to apply project properties to this drawing, and then it will become a part of your new project.
Continue like this until you have populated an entire project with the old vanilla stuff. After that, you will technically have an ACADE project with all of your old work. However, none of it has any intelligence. ACADE won't be able to garner any info from the blocks and other entities as they exist. That means no reports, no updates (except to the title block you made), etc. So you will now have to go through on a drawing-by-drawing basis and start tweaking things.
What needs to be tweaked? Depends on your specific needs, and this is where the rabbit hole gets deep. In order to use blocks, ACADE wants them to be named a certain way. If blocks aren't named according to the naming scheme mapped out in HELP, ACADE will pass right over them when it comes time to run a report or update. Also, it expects to see certain attributes inside blocks. These are actually what hold the data that appear in reports, and the data used by the software when running updates and other project-level commands.
Furthermore, 'wires' are a distinct entity in ACADE. They can only be lines, never a polyline or arc, and must be on a designated wire layer. Otherwise, the software won't recognize the line as a wire, versus some other graphical object. When you use the Insert Wire command, this is all done for you. But, with drawings that came from vanilla ACAD, you're in a whole different boat. There are commands available to convert lines to wires.
You may benefit from the Swap/Update Block command. For common symbols, such as circuit breakers or relays, this will work well and can be done across the whole project at once. Be aware, the block names matter. If you have a relay symbol on the first drawing that looks the same as one on the third drawing, but they have different names from one another, then the swap block command will only grab one. You'd have to run the command again for the differently-named relay. If there are any custom blocks in the vanilla stuff, you may need to recreate them in ACADE, or edit them in Symbol Builder before trying the swap command.
That covers most of what you're looking to do. Remember the rabbit hole and try not to get lost, lol.

Jim Seefeldt
Electrical Engineering Technician