Rather than linking to a file via a hyperlink, use the file attachment. That way we can easily replace old files and also view where a file is located on the website. In summary, do not hyperlink to PDF files.
When you upload a file attachment to a post, take a look at the link it creates. If there is a “_#” after the pdf file name, that means the file has already been uploaded. Remove that file and look for the file name in the file browser and use the original one.