input: Write a python function to extract text from a PDF file using PyPDF2.
  assert extract_text_from_pdf('sample1.pdf') == "This is the content of the first sample PDF."
  assert extract_text_from_pdf('sample2.pdf') == "Here is another PDF content."
  assert extract_text_from_pdf('sample3.pdf') == "Sample PDF number three with different text."
output: def extract_text_from_pdf(file_path):
      import PyPDF2
  
      with open(file_path, 'rb') as file:
          reader = PyPDF2.PdfFileReader(file)
          text = ''
          for page_num in range(reader.numPages):
              page = reader.getPage(page_num)
              text += page.extract_text()
      return text