To add file or folder size to it's name on disk.
Select file or files you want to modify.
Then select property - File Name
Select Action: Add / Insert
Renaming with file-folder size
Renaming with file-folder size. Previewing result
If your files are located in different nested folders and you need to rename files (add file size to the file name) but do not touch folder names. To do so, select folders where files are located, set Add / Insert action as described above, check Process subfolders check-box, in the Apply changes to box, select Files only.