If you are using from scrapy, then you may need to add a $
at the end of your regex:
[^ \t\n\r\f\v]+[\/]?(?<!\.pdf)$
If there is any way to use BeautifulSoup from your project, then try it:
htmls = '''<a href="adssad/asdasd/asd.pdf">M</a> <a href='asdasdasdas/asdasd/asdasd.doc'></a>'''
soup = BeautifulSoup(htmls)
for link in soup.findAll("a", {"href":re.compile("(?<!\.pdf)$")}):
print link['href']