Let’s look at important things here –
Mercury - Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
Purva Bhadrapada Nakshatra - It is a nakshatra related with mystical events and experiences. It is also nakshatra of duality. Please check this link for more info on Purva Bhadrapada Nakshatra - https://www.astrosaxena.com/pbnaksha.
Aquarius - As Purva Bhadrapada is part of Aquarius sign, Aquarius and things represented by Aquarius are also important here. Aquarius is 11th sign of zodiac belt, hence it signifies the things and energy related with 11th house of horoscope, such as Gains, Desires, Hopes and Wishes, Large Organisations, Network Circles etc. Besides this, Aquarius also represents Scientific Thinking & Research, Uplifting the Society, Higher Goals & Rewards for all. Aquarius is made of another set of 2 and half Nakshatra, i.e. Dhanishtha, Satabhisha and Purva-Bhadrapada. Aquarius Lord is Saturn & Rahu.
Pisces - As Purva Bhadrapada is also a part of Pisces sign, Pisces and things represented by Pisces are also important here. As Pisces is the 12th sign of zodiac belt, it represents the same energy and things which are represented by 12th house such as Isolated Places, Spirituality, Imagination, Other Dimension or Other World etc. Besides these things, it also represents your Hidden Talents, Ability to work in background, Spiritual Self etc. Pisces is consisted of last 2 and half nakshatra, i.e. Purva-Bhadrapada, Uttara-Bhadrapada & Revati. Pisces' lord is Jupiter.
Saturn & Rahu - As Saturn-Rahu co-rule Aquarius, their position and dignity is important to know about the overall functioning of any planet in Purva Bhadrapada/Aquarius.
Jupiter - As Jupiter rules Purva Bhadrapada and Pisces, its position and dignity is important to know about the overall functioning of any planet in Purva Bhadrapada/Pisces.
Houses Involved – Also, we can’t afford to forget the houses involved as a planet can be ruling different houses and sitting in different house for every person as per ascendant and planet’s position. To know overall affect, we have to consider the houses involved as those areas of life are being impacted.
Interpretation of Mercury in Purva Bhadrapada Nakshatra – Now, Mercury is in nakshatra of enemy Jupiter but in friendly sign. So, it is again kind of average dignity where person can get success in career but may feel the pinch in personal life. As Purva Bhadra is nakshatra related with spirituality and Mercury is business and communication, it shows someone who is involved in business or communication related with spiritual matters. We can easily see them as spiritual preacher and counselor. This result will be more prominent if Mercury is in Pisces portion of Purva Bhadra as Pisces is also a sign of Spirituality. In Aquarius section, they can be involved in business or entrepreneurship related with spiritual matters. As Purva Bhadra is also represented by a double-faced person and Mercury is clever/cunning in approach, at lower evolution level, it can very easily be creating a con-man or fraudster in spiritual matters. They can also be good at acting, deceiving people and mimicking others.
In relationship matters, things can be difficult as always because in Aquarius, Mercury is in Saturn's sign and in Pisces section, it is debilitated. As it is represented by double-faced person, it shows a split in relation or possibility of multiple relations.
Role of Saturn & Rahu - Also, Saturn-Rahu placement is important to guide Mercury in right direction, being Aquarius lords.
Role of Jupiter - Likewise, Jupiter placement is important to guide Mercury in right direction, being Pisces and Purva-Bhadra lord.
Other Factors – And of course, we need to consider conjunction, aspects, house lordship, house position and dashas etc to know the exact results of Mercury in Purva Bhadrapada. So, we always need to take a holistic view of chart rather than just 1 planetary position.
Conclusion – So, this is how I see Mercury in Purva Bhadrapada can work in a chart.