Problems with PyPDF2 and wand

I'm trying to show a preview of a pdf loaded via form.
I also share the error when I try to do python3 manage.py makemigrations
A help is greatly appreciated.

Python Version: 3.5
Django Version: 1.11

Now I share the code

models.py

from django.db import models  
from django.conf import settings
from django.utils import timezone

from PyPDF2 import PdfFileReader
from wand.image import Image
from .extra import ContentTypeRestrictedFileField

class Post(models.Model):

    author = models.ForeignKey('auth.User', on_delete=models.CASCADE)
    title = models.CharField(max_length=200)
    text = models.TextField()
    created_date = models.DateTimeField(default=timezone.now)
    published_date = models.DateTimeField(blank=True, null=True)
    pdf_file = ContentTypeRestrictedFileField(upload_to='pdfs',
    content_types=['application/pdf'],
    max_upload_size=5242880,
    )

    def convert_to_png(self, width=0, height=0):
        self.__convert_to_img__(width, height, 'png')

    def convert_to_jpg(self, width=0, height=0):
        self.__convert_to_img__(width, height, 'jpg')

    def __convert_to_img__(self, width, height, format='jpg'):
        size = ''
        if width and height:
            size = '_' + str(width) + 'x' + str(height) + 'px'

        filename = self.pdf_file.name
        filepath = settings.MEDIA_ROOT + '/' + filename
        output_dir = filepath + '_' + format + size + '/'
        os.mkdir(output_dir)

    def publish(self):
        self.published_date = datetime.datetime.now()
        self.save()

    def __str__(self):
        return ('<%s => %s: %s, %s>'%(self.__class__.__name__, self.author, self.title, self.text, self.created_date, self.published_date, self.pdf_file))

forms.py

from django.forms import ModelForm
from .models import Post

class PostForm(ModelForm):
    class Meta:
        model = Post
        fields = ('title', 'text', 'pdf_file')


    def __init__(self, *args, **kwargs):
        super(Post,self).__init__(*args, **kwargs)

views.py

from django.shortcuts import redirect
from django.shortcuts import render, get_object_or_404
from django.utils import timezone
from .models import Post
from .forms import PostForm

def post_new(request):
    if request.method == "POST":
        form = PostForm(request.POST, request.FILES)
        if form.is_valid():
            post = form.save(commit=False)
            post.author = request.user
            post.published_date = timezone.now()
            post.pdf_file=PdfFile(pdf_file = request.FILES['pdf_file'])
            post.save()

            # convert to jpg file after uploading
            # if you don't pass parameters then the images
            # will have the actual size
            post.convert_to_jpg()

            # convert to png file after uploading
            # if you need to resize the image just call specify it's size
            # like new_pdf.convert_to_png(200, 400) 
            # will return 200x400 px image
            post.convert_to_png(200, 400)

            return redirect('post_detail', pk=post.pk)
        else:
            return render(request, 'blog/post_edit.html', {'form': form})
    else:
        form = PostForm()
    return render(request, 'blog/post_edit.html', {'form': form})

def post_edit(request, pk):
    post = get_object_or_404(Post, pk=pk)
    if request.method == "POST":
        form = PostForm(request.POST, instance=post)
        if form.is_valid():
            post = form.save(commit=False)
            post.author = request.user
            post.save()
            return redirect('post_detail', pk=post.pk)
        else:
            return render(request, 'blog/post_edit.html', {'form': form})
    else:
        form = PostForm(instance=post)
    return render(request, 'blog/post_edit.html', {'form': form})

def post_list(request):
    posts = Post.objects.filter(published_date__lte=timezone.now()).order_by('published_date')
    return render(request, 'blog/post_list.html', {'posts': posts})

def post_detail(request, pk):
    post = get_object_or_404(Post, pk=pk)
    return render(request, 'blog/post_detail.html', {'post':post})

extra.py

from django.db.models import FileField
from django.forms import Form
from django.template.defaultfilters import filesizeformat
from django.utils.translation import ugettext_lazy as _

class ContentTypeRestrictedFileField(FileField):
    """
    Same as FileField, but you can specify:
        * content_types - list containing allowed content_types. Example: ['application/pdf', 'image/jpeg']
        * max_upload_size - a number indicating the maximum file size allowed for upload.
            2.5MB - 2621440
            5MB - 5242880
            10MB - 10485760
            20MB - 20971520
            50MB - 5242880
            100MB 104857600
            250MB - 214958080
            500MB - 429916160
    """
    def __init__(self, *args, **kwargs):
        self.content_types = kwargs.pop("content_types")
        self.max_upload_size = kwargs.pop("max_upload_size")

        super(ContentTypeRestrictedFileField, self).__init__(*args, **kwargs)

    def clean(self, *args, **kwargs):        
        data = super(ContentTypeRestrictedFileField, self).clean(*args, **kwargs)

        file = data.file
        try:
            content_type = file.content_type
            if content_type in self.content_types:
                if file._size > self.max_upload_size:
                    raise forms.ValidationError(_('Please keep filesize under %s. Current filesize %s') % (filesizeformat(self.max_upload_size), filesizeformat(file._size)))
            else:
                raise forms.ValidationError(_('Filetype not supported.'))
        except AttributeError:
            pass        

        return data

post_detail.html

    {% extends 'blog/base.html' %}

    {% block content %}
        <div class="date">
        {% if post.published_date %}
            {{ post.published_date }}
        {% endif %}
        <a class="btn btn-default" href="{% url 'post_edit' pk=post.pk %}"><span class="glyphicon glyphicon-pencil"></span></a>
        </div>
        <h1>{{ post.title }}</h1>
        <p>{{ post.text }}</p>
        <p>>{% post.pdf_file %}</p

    {% endblock %}