Validating the test from PDF is different then selenium library. You will need to use PDF libraries for python. One of the libraries I have used so far is PyPDF2.
Sample code:
import PyPDF2
pdf_file = open('sample.pdf', 'rb')
read_pdf = PyPDF2.PdfFileReader(pdf_file)
number_of_pages = read_pdf.getNumPages()
page = read_pdf.getPage(0)
page_content = page.extractText()
print page_content.encode('utf-8')
You can even try using textract library, if your PDF encoding is supported, extracting text will be very easy.
Sample code:
import textract
text = textract.process("path/to/file.extension")
Once your texts are extracted and stored into variable, you just have to assert it.