Python3 - Determing if a PDF is scanned or "searchable"
How about the PDF metadata check on '/Resources' ?! 

I believe for any text in a PDF (electronic document) there are more chances of having a font, especially the PDF, whose objective is to make a portable file, so, it maintains the font definition.

If you are a PyPDF2 user, try 

pdf_reader = PyPDF2.PdfFileReader(input_file_location)
page_data = pdf_reader.getPage(page_num)

if '/Font' in page_data['/Resources']:
    print("[Info]: Looks like there is text in the PDF, contains:", page_data['/Resources'].keys())
elif len(page_data1['/Resources'].get('/XObject', {})) != 1:
    print("[Info]: PDF Contains:", page_data['/Resources'].keys())

for obj in x_object:
    obj_ = x_object[obj]
    if obj_['/Subtype'] == '/Image':
        print("[Info]: PDF is image only")