Hi

Yes you can definitely become  district collector after your B pharma.

This is because,

UPSC civil services examination is your gateway for becoming a collector and now to be eligible for UPSC examination there's no need to be a graduate in a particular discipline,  all you need to be is a graduate in any discipline from a recognised university be it BAMS ,B. Arch, Btech, BSc, B pharma or any other course. So , you don't need to worry at all, after your B Pharma you will be eligible for UPSC

You can check UPSC eligibility criteria below

*You must have a bachelor's degree in any discipline   from a recognised university

*Minimum age limit :-  you need to be at least 21 years old to be eligible

*Maximum age limit :-  32 years , also there's 3 year relaxation on upper age limit for obc and of 5 years for sc/st category

For detailed information go through

https://competition.careers360.com/articles/upsc-ias-eligibility-criteria/amp

Thank you