Try PDFMiner. It can extract text from PDF files as HTML, SGML or "Tagged PDF" format.
The Tagged PDF format seems to be the cleanest, and stripping out the XML tags leaves just the bare text.
A Python 3 version is available under:
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…