因此，似乎是我尝试阅读的PDF出现了问题.但是，代码如下所示.感谢Thomas的带领. pdf的链接为" http://www.wine-economics.org/workingpapers/AAWE_WP16 .pdf "

So it seems that problem is with the PDF which I was trying to read. However the code goes like the below. Thanks Thomas for the lead. The link for pdf is "http://www.wine-economics.org/workingpapers/AAWE_WP16.pdf"

tt <- readPDF(PdftotextOptions="-layout")
rr <- tt(elem=list(uri="AAWE_WP16.pdf"),language="en",id="id1")
rr[1:15]