Hi, I agree with you, obsidian team should fix it and make it so that when you click on a the preview of a pdf on mobile it asks to open the actual file with the pdf reader of your choosing.
There is a workout though. Put the actual pdf in your attachment folder and on the side menu long-click it, click “share” and choose the app with which you want to open the pdf. It works.
Please obsidian team fix this.