Like most of you I frequently download/read PDFs and I use different apps for different purposes.
First, using my current work flow, I'd like the feature back that let's me truly choose whether to open or to save the PDF (pop up dialog). Currently, Edge Dev. either opens the PDF or saves it. (Settings: Always open PDF files externally) If I just want to quickly glance at a PDF I want to open it directly in Edge. If I want to read it extensively or want to annotate it I use specific apps.
Second, to make Edge my only PDF app I have some needs and preferences. I work on a Surface Pro 4.
For example, when reading my newspaper I prefer a horizontal page-by-page experience with a full screen reading feature. For this I use XODO. For other task where I need to highlight and/or take notes I put a print out to OneNote or use Drawboard PDF, which I also use if I only have to sign something quickly.
So to make Edge my default (and only) PDF app I'd like to have the following options:
Let me choose whether to open the PDF in Edge or to save it to a folder.
In Edge, let me choose whether to scroll vertically or to "swipe" horizontally.
Let me use my Surface Pen. I want to choose between some pens (highlighter, pen, pencil, etc.). They should behave like in OneNote.
Let me choose between a blank, lined or ruled "paper" as is possible in OneNote.