Wrtite-up Summary (link contains full solution)
Once connected to the server, you can extract the file hexdump with xxd:
xxd -ps 'De Monne Customer Portal.pdf' 
Save the hexdump in your local machine.
Use xxd -r -p <file of hexdump> > readable.pdf 
Now you can open the pdf file in your local machine and get the flag.
flag{deM0nn3_dat4_4_us}