Method using Google Colab only

1. Download your .ipynb file

You can actually do it using only Google Colab. File -> Download .ipynb

2. Reupload it so Colab can see it

Click on the Files icon on the far left:

Then Upload to session storage:

Select & upload your .ipynb file you just downloaded.

3. Get your file's path

then obtain its path (you might need to hit the Refresh button before your file shows up):

4. Conversion using %%shell

Then, just as in Julio's answer, execute in a Colab cell:

%%shell
jupyter nbconvert --to html /PATH/TO/YOUR/NOTEBOOKFILE.ipynb

The %%shell lets the interpreter know that the following script is interpreted as shell. Don't write anything before %%shell, use a distinct cell for this.

The form of /PATH/TO/YOUR/NOTEBOOKFILE.ipynb will be something like /content/lightaberration3.ipynb.

5. Your file is ready

Might need to click Refresh again, but your notebook.html will appear in the files, so you can download it:

The great thing about this is that nothing python-related has to be installed on your computer, not conda, not pip, only a browser.

I recently used BeautifulSoup and JSON to convert html notebook to ipynb. the trick is to look at the JSON schema of a notebook and emulate that. The code selects only input code cells and markdown cells

here is my code

from bs4 import BeautifulSoup
import json
import urllib.request
url = 'http://nbviewer.jupyter.org/url/jakevdp.github.com/downloads/notebooks/XKCD_plots.ipynb'
response = urllib.request.urlopen(url)
#  for local html file
# response = open("/Users/note/jupyter/notebook.html")
text = response.read()

soup = BeautifulSoup(text, 'lxml')
# see some of the html
print(soup.div)
dictionary = {'nbformat': 4, 'nbformat_minor': 1, 'cells': [], 'metadata': {}}
for d in soup.findAll("div"):
    if 'class' in d.attrs.keys():
        for clas in d.attrs["class"]:
            if clas in ["text_cell_render", "input_area"]:
                # code cell
                if clas == "input_area":
                    cell = {}
                    cell['metadata'] = {}
                    cell['outputs'] = []
                    cell['source'] = [d.get_text()]
                    cell['execution_count'] = None
                    cell['cell_type'] = 'code'
                    dictionary['cells'].append(cell)

                else:
                    cell = {}
                    cell['metadata'] = {}

                    cell['source'] = [d.decode_contents()]
                    cell['cell_type'] = 'markdown'
                    dictionary['cells'].append(cell)
open('notebook.ipynb', 'w').write(json.dumps(dictionary))

here is part of print(soup.div) output

div class="container">
<div class="navbar-header">
<button class="navbar-toggle collapsed" data-target=".navbar-collapse" data-toggle="collapse" type="button">
<span class="sr-only">Toggle navigation</span>
<i class="fa fa-bars"></i>
</button>
<a class="navbar-brand" href="/">
<img src="/static/img/nav_logo.svg?v=479cefe8d932fb14a67b93911b97d70f" width="159"/>
</a>
</div>
<div class="collapse navbar-collapse">
<ul class="nav navbar-nav navbar-right">
<li>
<a class="active" href="http://jupyter.org">JUPYTER</a>
</li>
<li>
<a href="/faq" title="FAQ">
<span>FAQ</span>

A screen shot of the resulting ipynb file, loaded on my local jupyter and after running all the cells

If you have LaTeX installed you can download as PDF directly from Jupyter notebook with File -> Download as -> PDF via LaTeX (.pdf). Otherwise follow these two steps.

1. For HTML output, you should now use Jupyter in place of IPython and select File -> Download as -> HTML (.html) or run the following command:

    jupyter nbconvert --to html notebook.ipynb  
   

   This will convert the Jupyter document file notebook.ipynb into the html output format.

   Google Colaboratory is Google's free Jupyter notebook environment that requires no setup and runs entirely in the cloud. If you are using Google Colab the commands are the same, but Google Colab only lets you download .ipynb or .py formats.

2. Convert the html file notebook.html into a pdf file called notebook.pdf. In Windows, macOS (brew install wkhtmltodf) or Linux, install wkhtmltopdf. wkhtmltopdf is a command line utility to convert html to pdf using WebKit. You can download wkhtmltopdf from the linked webpage, or in many Linux distros it can be found in their repositories.

    wkhtmltopdf notebook.html notebook.pdf   
   

Original (now almost obsolete) revision: Convert the IPython notebook file to html.

^{ipython nbconvert --to html notebook.ipynb}