Crop tool and/or keep page vertical position in scroll mode

[giammi56]

Dear all, In scroll mode with PAGE view, I am trying to set a custom page position which stays consistent at each turn of pages (i.e., left/right tapping), as in book mode. It is possible to fix the lateral postion, but a chosen vertical position is reset back to the beginning of a document page at each turn. Therefore, I tried to crop just the top of the page, but it seems not to work as intended:

1. When I enable the crop and set it to auto, there is no indication of how much it has been cropped; probably, it is cropped down to the visible content, but there is no progressive cut.
2. If crop tool is not enabled, top/bottom left/right sliders can be modified, the page is reloaded, but with not effect. Should they be greyed out when crop tool isn't enabled?
3. when cropped, the pdf quality is much degraded, but it is restored (i.e., sharper fonts) when zoomed in and out.

Is there a direct way to fix the zoom/crop of a page in scroll mode as in book? I have to work with this mode, because it is the only one allowing highlights and annotations.

Android 11 Librera PRO 8.5.37-fdroid (120)

Thank you!