它是固定的.实际上，没有任何问题.似乎我用来测试的pdf文件已损坏(即使我打开它时，内容也在那里，这就是为什么我一开始无法弄清楚的原因)

It's fixed. Actually, there wasn't any problem. Seems, the pdf I was using to test was corrupted one (even though when I opened it, the content was there, which is why I couldn't figure out at first place)

我用另一个替换它，它按预期工作.

I replaced it with another one and it worked as expected.