
Samsung GALAXY S4 Zoom LTE
Every official firmware build for SM-C105A, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/C105AUBUBOB1
Specifications of SM-C105, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-C105S

SM-C115W

SM-C1116

SM-C500X

SM-C5018
You can find the firmware on the model: SM-C105A page.
Yes, all firmware files for SM-C105A are 100% official, original, and obtained directly from Samsung servers.
To flash SM-C105A, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-C105A.