Just wanted to say many thanks to all posters here, esp TheK!
I installed AG3 on W10 (Hannari all-in-one, plus Darkhound's Illusion Wizzard and other mods) but it wouldn't run. I dropped in various downloaded d3d9.dlls and finally it ran OK, but no subs, stats, locations etc. Subtitles.cfg file was missing too.
After finding this thread, I downloaded dgVoodoo2_71_2 which is free and doesn't need installing.
I copied the D3D9.dll (386KB) from the dgVoodoo MS x86 folder into the AG3 install folder and renamed it to d3d9_alt.dll.
Probably unnecessary, but to be sure I then also replaced the d3d9.dll which I'd got the game to run on with the dll I'd used on the old PC (only 73KB).
On first launch a Subtitles.cfg file was created and AG3 runs perfectly - including the cheats overlay (which I haven't used!).
I thought some details might be useful for anyone still struggling to run AG3 on W10, -esp the dll sizes, as there are a lot of d3d9.dlls out there.
Shame about HF tho.