Deploying this in my Sharepoint organiztion was a terrible mistake. All I wantedto do was to be able to edit a fillable PDF and save directly back to the Sharepoint site. Your workaround (I assume you double clicked a PDF or chose Open in Adobe Document Cloud... is to click the vertical elipsis....chose Open...Open in Broswer
We are having the same issue, and yes that is our workaround for now which is to click on the ellipses and choose to open in browser.
However i would like to change the default behavior for opening PDF in SharePoint Online from opening with Adobe Document Cloud to open in browser.
I am aware on the answer here SharePoint - default open PDF option - can this be changed? but this does not help in our situation
I have already approached Microsoft Support and they say they cannot support the issue since it's not their product.
If someone manages to find a way or know how to change the default behavior then that would be great