- delete the alias in Finder, the alias is deleted but the original PDF in Finder remains.
Correct, because it’s just a pointer to the file.
- delete the indexed file alias in DevonThink → the original PDF in Finder is deleted.
The alias is resolved to the original document, as aliases aren’t supported.
Finder aliases are not recommended for use in DEVONthink.
They will not import and their use in indexing is limited and very specific in behavior, as you see here…