如何用后台进程从TWebBrowser打印PDF文件？

unit PrintPDF;

interface

uses
  System.Classes, Vcl.OleCtrls, SHDocVw;

type
  TPrintPDFThread = class(TThread)
  private
    FWebBrowser: TWebBrowser;
  protected
    procedure Execute; override;
  public
    constructor Create(WebBrowser: TWebBrowser);
  end;

implementation

{ TPrintPDFThread }

constructor TPrintPDFThread.Create(WebBrowser: TWebBrowser);
begin
  inherited Create(True);
  FWebBrowser := WebBrowser;
end;

procedure TPrintPDFThread.Execute;
var
  OleObject: OleVariant;
begin
  // 获取PDF文件的Ole对象
  OleObject := FWebBrowser.OleObject;

  // 打印PDF文件
  OleObject.Print;
end;

end.

procedure TForm1.Button1Click(Sender: TObject);
var
  PrintThread: TPrintPDFThread;
begin
  PrintThread := TPrintPDFThread.Create(WebBrowser1);
  PrintThread.Start;
end;