If there is a existing file new.png, the device automatically adds a (1) to the file, e.g here: new(1).png. What is the returned file Name in the Download Complete event? The given Save File As or the created file name existing in the device?
Its better to try yourself.
Checks whether a file or directory exists.
Prefix the filename with / (i.e. relative path) to look for the file on the SD card. For instance /myFile.txt will look for the file /mnt/sdcard/myFile.txt. To read assets packaged with an application (also works for the Companion) start the filename with // (two slashes). If a fileOrDirectoryName starts with file:/// you can specify a complete path to the file of directory."
Taifun Extention link here
I tested and unfortunately the file name is the one assigned by the system if the name already exists.
good idea, but this one does not face my issue.
Use do it to find out what Download Complete event returns.
Tip 4 - App Inventor: How to Learn | Pura Vida Apps
Something like this