How to get apk files of apps after installing them from Google Play Store ?

1. install "ASTRO file manager" into my mobile phone
2. run ASTRO app
3. open left side menu by touching Arrow icon on upper-left side
4. select "Tool" menu by touching lower-left side icon
5. select "App manager" in Tool menu
6. select the app that you want to backup in the list of  installed app
7. select "Backup" in the bottom menu
8. connect phone to PC with USB cable
9.  select Mobile phone storage disk driver and the select "Internal Storage" folder by using "File Manager" in Windows
10. Browse apk file item in that folder, such as "com.cousinHub.PFChartsWidget.apk"

或是

如何將已經安裝的app備份成apk？


    在手機中安裝「ES檔案瀏覽器」軟體。執行軟體後，按下左上角選單功能/庫/程式，長按要備份的軟，點選下方的「備份」。備份的預設路徑為："sdcard/backups/apps/"。