Recommend lightweight Apps for android

Can you guys recommend free lightweight android apps for pdf reader(only reading, if it can read .txt files that would be a +) and a music player (only playing music and organize tracks by date, if it can also play video files that would be a +)
My phone is a samsung galaxy star duos gt-s5282.
Thank you.
Answer #1
adobe reader will do the trick for you
And music player. Use free version of DOUBLE TWIST. It’s awesome.. It’s UI is easy to organize Love it
Answer #2
moon reader and spotify