It is a legal document. Under the law, your landlord must demand that you vacate at least 10 days prior to going to court. Clock started running, I suspect.
This was an attempt by your landlord to post a "Notice to Quit". Such Notice may (or may not) be required under your lease. I strongly recommend you review your lease to determine how your landlord is require to proceed with a Eviction action. Then, prepare for the next phase. either move out or you should expect an Eviction Complaint will be files with your local Magisterial District Judge.
It might also be time to pay a lawyer for 30 minutes of his/her time to review your options.