Default to have thumbnails show up
I used to be able to have thumbnails show up every time I open a .pdf. I open very large file all the time, so it's very nice to be able to set thumbnails to be visible as a default instead of having to request it with each new document
Hope below steps work for you :
1) Launch any PDF and Expand the Panel that you want the acrobat to open by default for every document(For Ex. Page Thumbnails)
2) Right click on the LHP Navigation strip , Select the option from the context menu "Pin Page thumbnails" .
3) now try out by launching any other pdf -> You will observe that the Page thumbnails panel would appear expanded by default on launch(If document does not have any other document specific preference )
Let us know if it works.