The intended usage of this tool is for unreal developers to create patches and add-on content cocked with the editor. The List & Extract feature is just for validating packed files, not for the purpose of unpacking & repacking or modding.
This is for finding the UnrealPak.exe executable. It's the path containing unreal's Engine folder, i.e. D:/UnrealEngine/UE_4.26. Alternatively you can copy your UnrealPak.exe to the folder where UnrealPakGUI.exe is and leave this field empty.
This is for encrypting/decrypting your pak file. If encryption is not necessary, leave it empty. This file can be found in the Saved folder under your unreal project directory after having packed your project at least once in editor with a crypto key.
Self-explanatory. This is for getting the project name. Required for the Content Files Only option;
If checked, only files under "Content" and its subfolders are packed, so the pak mount point will be set to ../../../<ProjectName>/Content/*. Otherwise mount point is set to the common root directory of the input files. This is intend for the usage where you want to pack cooked assets in the Saved/Cooked/WindowsNoEditor/<ProjectName>/Content folder with a valid mount point.
Self-explanatory. Check this if you want to compress your pak file.
Self-explanatory. Requires a valid Crypto.json file.
Create a single pak file from the list. Add files/folders by dragging them onto the list. Remove files/folders by selecting them and click Remove or Clear the list by clicking Remove All. Click Create Pak to start packing.
Batch creating pak files to the Output Dir.
Option As Patch - If checked, a suffix _p will be added to each created pak file. Pak files with the _p suffix are considered patches by unreal engine. Contents in a patch pak file will override those in the original game pak file.
Option Folder Pak - This is an ease-of-use option. The default behavior of drag & drop is creating a pak file for each drag & drop operation. If this option is checked, a pak file will be created for each folder in a single drag & drop operation.
List pak contents by drag & drop pak file onto the list. Optionally extract its content to the Extract To directory. If the pak file is encrypted, then the option Encryption should be checked and a valid Crypto.json file must be provided.