There is not enough space on the disk when there is?

Solution 1:

I had a similar problem with a Windows client trying to access a Linux server. I shared a folder that had mounts from different disks. The problem and solution are described in this answer: https://askubuntu.com/a/631977/535528

in short the solution is to share the individual disks, rather than some parent where those are mounted. This will also result in exporting multiple shares instead of one from the samba configuration.

Solution 2:

It is likely that a quota has been set on the pdf_docs directory.

Directory quotas are configured using the File Server Resource Manager tool. You must be an administrator on the file server to use it.