We have two servers (client-facing, and back-end database) between which we would like to transfer PDFs.  Here's the data flow:

User requests PDF from website.
Site sends request to client-server.
Client server requests PDF from back-end server (different IP).
Back-end server sends PDF to client server.
Client server sends PDF to website.

1-3 and 5 are all good, but #4 is the issue.
We're currently using Flask requests for our API calls and can transfer text and .csv easily, but binary files such as PDF are not working.
And no, I don't have any code, so take it easy on me.  Just looking for a suggestion from someone who may have come across this issue.
I wanted to share my solution to this, but give credit to @CoolqB for the answer.  The key was including 'rb' to properly read the binary file and including the codecs library.  Here are the final code snippets:

Client request:
response = requests.get('https://www.mywebsite.com/_api_call')
Server response:
f = codecs.open(file_name, 'rb').read()
 return f
Client handle:
with codecs.open(file_to_write, 'w') as f:
    f.write(response.content)
    f.close()

And all is right with the world.
Transfer PDF files between servers in python