[Casimiro Noteví]

Por ejemplo, con synPdf

Código Delphi [-]
uses
  SynPDF;

function GetNumberOfPages(const FileName: string): Integer;
var
  PDF: TPdfDocument;
begin
  PDF := TPdfDocument.Create;
  try
    PDF.LoadFromFile(FileName);
    Result := PDF.PageCount;
  finally
    PDF.Free;
  end;
end;