If I put a placeholder such as %date% in a Markdown document, save the document in the Templates.noindex folder, and use the Data ➜ New from Template menu item to create a new item using the template, the date gets filled out as expected. If I do the same thing with an OmniOutliner .ooutline document, it does not.
What are the file/document types in which DEVONthink will perform placeholder substitution?
Omnioutliner documents aren’t editable in DEVONthink. This is true of any proprietary format, like Word, etc.
Oh, of course, that makes sense. Thanks.
You’re welcome.
PS: in the past, I’ve tried that kind of thing too. 
Can I use a placeholder in a Formatted Note? I had done it in an RTF Note and it works but it doesn’t seem to work in a Formatted Note. Is that the expected behavior?
Plain/rich text, Markdown documents, sheets, HTML pages and formatted notes support placeholders. See also Insert Placeholder submenu in contextual menus.
Thank you.