The old S5 software was CPM based, and the DOS version was just the same CPM with a small com file that run CPM emulation in dos.
Even that did not work very well on windows. IBH was written for windows and was a system not written by Siemens but was pretty good. Step 7 can convert S5 files but if there are some used FB's it creates blank ones as they are not compatible with S7, this applies to some additional FB's you could purchase from Siemens. I bet someone on here has S5 and if you post them the code they could create a PDF for you