THPDFJSONValue.SetTextMember

Writes an object member as a Unicode string, replacing any existing member sharing the same key

procedure SetTextMember(const Key: AnsiString; const Value: UnicodeString);

The unit is HPDFDocJobs; the text is stored such that GetText hands it back unchanged

Reach for SetStrMember when the source is already UTF-8 bytes

Member keys are UTF-8 bytes and are case-sensitive