If you're trying to create "stationery templates for digital download", surely the point is that the users could then use those templates in Word, for example? Creating them as PDFs would be rather pointless, since whoever downloads them couldn't use them as templates before converting them to a suitable word-processing file format.

You'd only use PDFs with fields if the intention is for users to do more than fill in some blanks - but then you're not really distributing templates but fillable forms. If that's what you intend, you could use LibreOffice's Writer application, instead of Word, to create the document. As I understand it, formfields created in LibreOffice's Writer convert to functional PDF fields when saved in that format. Word's inability to do so is probably related to licensing issues with Adobe.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]