Add/upload files from/to another folder than upload

Hi,
There are lot of files I have to attach, mostly PDF and Docx, but all of theme are located in another folder for example “files” and it’s subfolders “cat1, cat2, …”, I don’t want to mess the files by uploading theme to WordPress date based upload folder, I need to keep the files and folders structure and attach them to posts using Document Gallery, Would you please help me how can I do this?

Thanks