1. Does this mean he was born free

Not necessarily. Your ancestor may have been born a slave and freed, or he may have been freeborn.

2. Why were these kind of papers needed?

The papers were required to show proof of free status. In slave states, the status of African Americans was assumed to be that of a slave. So if free, he/she had to show proof of that status, or be considered a possible fugitive or runaway slave. Although the analogy isn’t quite equal, it would be like having to keep
a passport to show proof of American citizenship. In the case of a free black, the paper would show proof of free status under whatever terms—birth or emancipation.

Although I am not familiar with Maryland laws respecting free papers, I do know that in neighboring Virginia, free papers had to be renewed on an annual or triennial basis. However it is hard to determine how regularly people complied with the laws, as court records suggest that few people did so. What I’ve found however, was a tendency amongst free blacks who traveled outside of their communities to have their free papers/registers renewed regularly. Another tendency was for people to be required to renew their papers during a time of unrest, or high runaway activity. Typically those who lived in cities were required to renew their papers more frequently than those who lived in surrounding counties and rural areas.

3. Does this mean he was the child of slaves? (or ex slaves?)

Not always. The papers usually specified the manner in which the certificate holder established or claimed his free status.

You would have to check on Maryland laws and then more locally, Charles County, to see who was required to carry those papers. Perhaps in the beginning, probably only those who were emancipated had to show proof. Later perhaps both free born and emancipated people had to show proof of their free status.

The laws were enforced more strictly in Virginia following Nat Turner’s uprising in 1831. Maryland followed suit and adopted similar measures. The timing of your ancestor’s paper points to the necessity of such a document. 1835 was a particularly violent year filled with anti-abolition physical attacks on travelers. Those traveling south from any northern city were under high suspicion. Seeing that your ancestor traveled to Philadelphia, a hotbed for abolitionism, he needed the documentation to vouch for his character and that he wasn’t an abolitionist.

4. What is a certificate of personal knoweledge? Why would this be needed?

The certificate or paper of personal knowledge was a form of protection for the free black. It was composed by a prominent white person or persons who had personal knowledge of the certificate bearer. Some of these certificates contained detailed information such as a physical description, birth status, parents, occupation and residence.