SelectAll procedure

Selects every character on the page(s) currently displayed by the viewer.

Builds a selection spanning every character of the current page. In spread display modes (dmTwoPageContinuous, dmTwoPageContinuousWithCover) and when the right-page index is in range, extends the selection across both visible pages so the user gets the full content of the visible spread — including a CR/LF joiner between the per-page slices when round-tripped through SelectedText.

Degrades to a single-page selection on the last odd page of a spread display, or when the right-page text is empty.

• Available since v1.36.0.
• Code-level API — always works regardless of AllowUserTextSelection (which only gates user input).
• Wired to the Ctrl+A keystroke when AllowUserTextSelection = True and no form field has focus.
• Setting the same selection twice does not re-fire OnSelectionChange.

ClearSelection, HasSelection, SelectionCharCount, CopySelectionToClipboard