Adding File as a Attachment
ERPNext allows to attach files with documents. User with a read permission on particular document will also be able to access files attached with it.
Attach New File
There are several ways to attach file to the document.
By drag and drop
Click on Attach to browse and select the file.
If you use separate server for files, or use online service like Dropbox, you can attach file by providing link of a particular file.
For hosted users, limit of 5 MB is applied on file size.
To ensure there are not many files attached to a document, which can affect your accounts performance, you can set limit as how many files can be attached to a particular document. Click here to learn more about it.
Check following link to learn how files are managed in ERPNext.