Program files is protected area for custom config the PSpad

The default folder for install PSpad is Program files, that is protected from making of the custom configuration without windows lead.

I recommend to use the Total Commander's experience and change the default folder in installation pack to c:\PSpad

Which custom files do you mean?
As default (if not installed as portable), PSPad stores custom files in %APPData%\PSPad

If you need (not regularly) change some files in Program files, you can run PSPad as admin

My and my student's installations are full and they default installs into Program file directory.
1 The custom syntax highlighting the files Syntax/*.ini located in the root directory of PSpad and Windows dissmiss to create custom syntax- schema.
2 When PSpad run to close a Windows disabled it to write the last configuration
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Only moving the folder "PsPad editor" outside from "Program files" leave the editor and users from it's control
///////////////////////////////////////////////////////
the windows warning from default folder Program files is here:

Problem signature:
Problem Event Name: APPCRASH
Application Name: PSPad.exe
Application Version: 5.0.7.775
Application Timestamp: 6415d06f
Fault Module Name: KERNELBASE.dll
Fault Module Version: 6.1.7601.17617
Fault Module Timestamp: 4dce2b0e
Exception Code: 0eedfade
Exception Offset: 000000000000cacd
OS Version: 6.1.7601.2.1.0.256.48
Locale ID: 1029
Additional Information 1: 0912
Additional Information 2: 0912fa3bb72a165e66c76851615ab572
Additional Information 3: 07d7
Additional Information 4: 07d775d612f713599fae0bb048cb61b5

Read our privacy statement online:
go.microsoft.com

If the online privacy statement is not available, please read our privacy statement offline:
C:\Windows\system32\en-US\erofflps.txt

I understand. There are 2 requests what goes against itself:
1. admin needs to have clear install (even own) without touching it by users
2. admin wants users let change installation (your case)

Your situation is soluble by installing PSPad out of Program files folder (as you suggested) or setting write rights into Program Files\PSpad folder (and child objects) for users

Problem is: there are no in the Installation pack of the prompt to select the folder where to install the PSPad.

When you install it first time, there is a prompt. When you update (next time of installer), there is no prompt.
If you want run PSPad from e.g. C:\pspad, you can use ZIP and unpack it there.
ZIP is full installation.