Also see  Issue 847039  which is a similar issue under My Drive instead of Downloads.

Chrome Version: M68 or later.
OS: Chrome OS

What steps will reproduce the problem?
(1) Create a PDF file. Rename it containing full-width space. for example: "ファイル　その１.pdf"
(2) Double click the file.

What is the expected result?
The file is opened in a browser.

What happens instead?
The browser fails to open the file, with following error:
  "Your file was not found
   It may have been moved or deleted.
   ERR_FILE_NOT_FOUND"

 

Also see  Issue 847039  which is a similar issue under My Drive instead of Downloads.

Chrome Version: 67.0.3396.99
OS: Chrome OS

What steps will reproduce the problem?
(1) Create a PDF file. Rename it containing full-width space. for example: "ファイル　その１.pdf"
(2) Double click the file.

What is the expected result?
The file is opened in a browser.

What happens instead?
The browser fails to open the file, with following error:
  "Your file was not found
   It may have been moved or deleted.
   ERR_FILE_NOT_FOUND"