Yes, I was able to upload the filled copy only after I followed the described method
Here is the trick. I will try to be as simple as possible
1. open your application page and copy the link of the file. You can do this in many ways such as
a. Right click on the link (the name of the file) and select "copy link" from the options or
b. Open the file in a new tab and copy the link from the browser address bar
2. Launch/open your acrobat reader (that's what I used, other pdf readers may be able to do the same)
3. click on open and paste the link you copied from the browser address bar into the section named, "filename" at the lower part of the open dialogue box
4. Click on open. This may take a while depending on your internet speed. The file will be downloaded into your system.
5. Fill and validate it and save it on your system using "save as"
6. Go back and upload it. This worked for me and should work for you.
For online application, you are not required to sign on the form. You are expected to provide your signature during the submission online.
Don't hesitate to contact me again should encounter any other issues
Regards