Worked very well for me.
The only odd was that the files are stored in other folders (other structure)
into the server. All files was then downloaded in a different folder. For
example:
The structure in website is shown:

<https://site.com/groups/group_name/files/>
+---folder_A
|      file_01.pdf
|      file_02.pdf
+---folder_B
|      file_01.pdf
|      file_02.pdf

But, when (mouse) pointing to the supposed file:

<https://site.com/groups/group_name/files/folder_A/file_01.pdf>

it showed me an address like:

<https://xxx.com/yy/group_name/file_01.pdf?token=gEKAUcYLwHnhn9L3p_fQUr_dsqkKLRpP9foPGbyOrExRQ4L7j97FHDoO30smy5iZnOSB0vodjHT5RZZCvgvqLlGgLEvaEYY3wbvflGd6KUIrYtPhwg&type=download>

After mirroring, the strucure below is created in httrack structure:
.../group_name/files/
+---folder_A
+---folder_B

but there are only index.html files.

And the pdf files are all located in just one folder, but with appended  with
strange characters, like:

.../yy/group_name/
|      file_01eKp9.pdf
|      file_01Fpo4.pdf
|      file_02ddDc.pdf
|      file_0234qp.pdf


Of course, opening the (locally) mirrored website and opening this html:
httrack_folder/.../group_name/files/folder_A/index.html
is presented the file_01.pdf, but its linked to:
httrack_folder/.../yy/group_name/file_01eKp9.pdf
instead of 
httrack_folder/.../group_name/files/folder_A/file_01.pdf
or
httrack_folder/.../yy/group_name/files/folder_A/file_01.pdf 
or even
httrack_folder/.../yy/group_name/files/folder_A/file_01eKp9.pdf 

Someone knows if its possible to download the files in the same structure
presented in website (folder_A/file_01.pdf folder_A/file_02.pdf
folder_B/file_01.pdf folder_B/file_02.pdf)?For few files its not a problem,
but there are too much.