AppleScript Opening iCloud Documents
You’re trying to define the filePath variable by combining a Posix path string with an HFS string.

Try defining the filePath variable like this…

set filePath to (path to library folder from user domain as text) &amp; ¬
    "Mobile Documents:com~apple~Numbers:Documents:Budget.numbers"

tell application "Numbers"
    open alias filePath
end tell


OR.. My Personal Preference

property theDocument : "Budget.numbers"

set filePath to ((path to library folder from user domain as text) &amp; ¬
    "Mobile Documents:com~apple~Numbers:Documents:" &amp; theDocument)

tell application "Finder"
    if not (exists of alias filePath) then
        tell current application to display dialog "The File: " &amp; theDocument &amp; ¬
            " Does Not Exist" buttons {"Cancel", "OK"} default button "OK"
        return
    end if
end tell

tell application "Numbers"
    open alias filePath
end tell


If you’re not quite sure how to correctly define a file path, you can always use the following Apple Script code in a separate script editor document to correctly retrieve the file paths

set filePathAsAlias to (choose file with prompt "choose file") -- Returns The File Path As An Alias


OR

set posixPathOffilePath to POSIX path of (choose file with prompt "choose file") -- Returns The POSIX Path Of The File