[maestralien]

It seems not possile to write annotations behind the arrows (previouis/next page) at the bottom-left ... any workaround or solution to solve this situation?

[Geoff Bacon]

On the top menu bar when editing, press the icon that, to me, looks like an old VCR tape (if you know what that is! - 4th icon from right) 
This will change to a different arrows display and you can drag it around to where you want it.

I've only just found this when researching your question. I typically insert text somewhere near the arrows and then use the nudge tool to move it into position.
Also for text, the arrows are removed when the virtual keyboard is displayed
I suspect that you will need to use the "VCR" icon if annotating with the other tools

Geoff

[Zubersoft]

The command bar icon (the one Geoff is referring to) will display a toolbar with additional shortcuts, which hides the little toolbar at the bottom left. That's one way to get to the page under those arrows. Alternatively, select the panning tool in the toolbar, then just move the page up or down as needed. 

Mike

[maestralien]

On the top menu bar when editing, press the icon that, to me, looks like an old VCR tape (if you know what that is! - 4th icon from right) 
This will change to a different arrows display and you can drag it around to where you want it.

Geoff

Thank you Geoff, this is a good solution. Although, that "tape" looking like icon is the 11th from right in MobileSheets Windows version

[maestralien]

The command bar icon (the one Geoff is referring to) will display a toolbar with additional shortcuts, which hides the little toolbar at the bottom left. That's one way to get to the page under those arrows. Alternatively, select the panning tool in the toolbar, then just move the page up or down as needed. 

Mike

Thank you Mike, the additional panning tool solution is also useful.