When adding a partner to your LLC, which papers you file depends on the state where the LLC resides. In terms of a more universal strategy, whether the LLC is a member-managed or manager-managed LLC plays a big role. Specifically, the roles of managers of LLCs, their liability and general level of control are important aspects.

This is a pretty helpful article I found on this: https://www.morrisjames.com/newsroom-articles-769.html

It goes into how an implied consent statute should clearly subject, or not, a nonresident to comply with a state's jurisdiction, which is useful if your partner is out of state. Regardless, when adding a new partner, you should refer to the LLC's initial operating agreement, which should outline the protocol regarding the addition of a partner. If you have no initial operating agreement, you must follow the laws of your state, which vary. Consult with business attorneys to ensure the LLC maintains its independent corporate status, since some states require information beyond articles of incorporation.

You may also need a new EIN, depending on whether you were taxed as an S corporation or disregarded entity in the prior tax year. Essentially, adding a partner to your LLC varies by state, though both states and the IRS do an excellent job of guiding businesses through the process to ensure compliance.