Well, the easiest course is to contact the executor and ask your questions. But, remember, the amount of information that the executor is legally required to provide you is limited. Also, you can always contact the Orphans' Court in the applicable county to ask if you can get a copy of the probate file.
Did you just receive a copy of the Petition? When was the will submitted? If it was only a few months ago that probate was opened, making distributions already is lightning speed.
Have you received anything else from the executor? Estates in PA can be closed in three ways:
1) With a formal accounting submitted to and audited by the court together with a petition to the court to close the estate. If that is the route taken, you should receive a notice that the accounting is being submitted.
2) By what is often called a family settlement agreement which is less expensive than going the formal accounting process. The agreement basically says that all the beneficiaries agree with the handling of the estate and are OK with closing the estate. While I do not think that it is required, usually a copy of the estate inventory and a accounting accompany the agreement. If those aren't included, the beneficiary can refuse to sign and insist on a formal accounting.
3) If the gross value of the estate is less than $25,000, the executor can simply petition the court to permit distribution.
Keep in mind that the amount on the Petition is an estimate. If the property was sold, then the distribution will reflect the actual net sales proceeds after all the deceased's debts and estate administration expenses are paid.
Nothing requires that the distributions be sent by certified mail. But it is a good practice.
Even if the estate is not subject to federal estate tax, PA has an Inheritance Tax that applies to almost all assets transferred from the deceased's estate to beneficiiaries. Normally, the executor files the return and pays the tax from estate assets before any disttributions are made.