Solution: You downloaded a trial version. Look for "Freeware" or "Open Source" tags. For reliable free merging, use Microsoft Paint 3D (build into Win10/11) or Apple Preview (built into Mac).
Some free versions add a watermark during merge unless you sign up. image compress merge sign software download
Download the audit report for an agreement - Adobe Help Center Informative Report: Image Compress, Merge, and Sign Software
While few single-function "image" apps handle all three (compression, merging, and digital signing) in one interface, these professional suites do: OS: Windows 10/11, macOS 11+, Ubuntu 20
: A reliable utility available on SourceForge and the Microsoft Store. It is specifically designed for high-volume optimization, watermarking, and resizing.