function SelectedText: WString;
Extracts the text under the active selection through FPDFText_GetText and returns it as a Unicode string. In spread cross-page selection, the per-page slices are joined in page-ascending order with a #13#10 (CR/LF) separator so the round-tripped text reads like normal multi-line content.
Returns the empty string when nothing is selected.
FPDFText_IsGenerated) appear in the result as their literal characters — same convention as the lower-level Text(Start, Count) API on TPdfView.ShowMessage(string(PdfView1.SelectedText));