I don't really do manual downloads I'm afraid. It ends up being too much of a security concern. You can feel fairly safe that when someone uploads malware to Steam that you will have a solution. But a random file on the internet that someone loads to Dropbox or whatever?

Here's the deal though: you can make the Steam download more reliable with a few tips:

1) Subscribe to the mod

2) Navigate to your Steam installation folder. (let's say it's windows/program files/steam). If you have no idea where this is then use windows search.

3) Navigate two more level down to steam/userdata/#######/ugc/ referenced /
The ####### is going to be a string of numbers. You should only have one folder like this on your machine.

4) Steam keeps files here that it downloads from mods. If you look around in the folder you will see several folders with long strings of numbers as file names (for example a folder called ‘507028274407570926’). Inside those folders will be another folder called ‘mod’ and inside that is a.zip file. The .zip files contain the mods that you have subscribed to but Steam has not yet installed. Find the one with called contest_europa.zip

5) Copy the contest_europa.zip file into your /mods/ folder. Then save a second copy of it to a new folder that you create in the /mods/ folder named ‘Contest Europa’

6) Unzip the contents of the .zip file in the folder you just created (winzip works great if you don't have a program)

7) You will now see a number of folders that the mod uses for data as well as a file ‘descriptor.mod’ This ‘descriptor’ file is the mod file which alerts EUIV to your mod.

8) Open up with descriptor file with Notepad++ or Wordpad, some text editor like that.
The first two lines will be:
name="Contest Europa"
archive="mod/Contest Europa.zip"
If you see that you are in the right place.

9) Now, exit out of that ‘descriptor.mod’ and rename it as ‘Contest Europa.mod’
You’ve now got a folder you created called ‘Contest Europa’ with a bunch of mod folders in and one .mod file which is labeled ‘Contest Europa’

10) Copy the .mod file and paste a copy into your /mods/ folder.
That’s it, you’re done. You have now successfully outwitted Steam and manually installed the mod. This works for any EU4 mod you download from Steam. (Really any mod on Steam, although you may have to tweak a few things)