You can't claim adverse possession — you haven't owned it long enough. The previous owner could have, but didn't. That is not something that passes on to the new buyer (you).
Understand what adverse possession, and is not. Adverse possession is not a grant of ownership after 21 years, it is a statute of limitation that holds the "true" owner no longer gets to claim the possessor is not the owner. In other words, after 21 consecutive, open, public years of possession the true no longer gets to kick the possessor off because they have ceded ownership of it.
When the previous owner sold to you, he abandoned his claim to the disputed property. The clock then starts running from zero on your claim.
You should speak to an attorney. Pennsylvania recognizes the legal concept of "tacking" whereby you can use the previous adverse possessor's time to count toward claiming adverse possession yourself.
However, the possibility of a claim for adverse possession doesn't automatically you get the 10' strip of land - you need to go to court and follow proper procedures before you actually own the land (in other words, the passage of time, in and of itself, is not enough to actually take the land). Further, adverse possession requires more than just the passage of time (for instance, your use must be "adverse" to the rightful owner, open, notorious, etc...).
Since there are many variables involved with adverse possession, you would be best to consult with a local attorney before doing anything.
Licensed in MD, PA and DC. This is not legal advice. I am not your attorney until we have mutually agreed that I am your attorney. You should consult with an attorney licensed to practice in your jurisdiction regarding your specific circumstances.
You have comments from two lawyers. The comments regarding "tacking" are important. When making a claim of adverse possession you may "tack" together your time in possession with that of a predecessor ONLY if your deed adequately describes the property you are claiming. You can never win an adverse possession case without a survey or legal description of the property your are claiming. If you have that description, and your seller is still alive, try to get him or her to give you a quit claim of his or her interest in the land.
DO NOT ask the neighbor to give you a deed. Doing so is proof that you fail in one of the elements of adverse possession.
You must also remember that there are fall back positions (boundary by consent, prescriptive easement, etc) that must be considered.
This is a complex area of the law. Find someone who knows it well. If they have not taken the course Boundary Law in Pennsylvania, be suspicious.
DISCLAIMER The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the Commonwealth of Pennsylvania. Responses are based solely on Pennsylvania law unless stated otherwise. When answering questions on AVVO, attorneys are prohibited from directly soliciting business. Don't take this as an indication of lack of interest. James S. Tupitza 212 West Gay Street West Chester, PA 19380 610-696-2600