Those are in-universe classification levels. It says low-level personnel are not allowed to access this file, only Level 4 and O5, the latter being the top tier Foundation ruling council. So that one can't really be decoded without a bit of SCP-specific knowledge.

O5: http://www.scpwiki.com/o5-command-dossier

Access to information restricted to Level 4 clearance and O5 council only.

Probably that the data contained therein is authorized for foundation members at O5 and O4 level

http://www.scpwiki.com/security-clearance-levels

This part is talking about who is allowed to view the materials. Level 4 and O5 are the top people of the foundation and the information is only allowed to be seen by them.

Information must only be shared with those of level 4 clearance or higher.

Edit: Oh wow, a lot of people replied between my last page refresh.

Information about this SCP is not to be given to anyone with a clearance level below level 4. (Including the O5's)