It just closes

[pinguluk]

When I try to open a .pak, it just closes.

[jashking]

you can see the log to find why it crashed

[pinguluk]

I can't find the log, where can I find it?

[jashking]

if you use the pre compiled version: C:\Users\[YourAccountName]\AppData\Local\UnrealPakViewer\Saved\Logs
else Engine\Programs\UnrealPakViewer\Saved\Logs

[pinguluk]

UnrealPakViewer.log

[jashking]

the precompiled version was compiled with UE 4.26.0, which max compatible pak file version is 10, and can't open pak files which version is 11, so you have to compile UnrealPakViewer by yourself