I created a formatted note document in DEVONthink To Go and pasted in an image from my photo library. The document displays in the Sidebar as 28.8 MB in size, and the Preview pane shows nothing other than ‘Document too large’. Any reason why this would be too large to display? iPad Pro, plenty of free space available, iPadOS 13.3.1.
BTW, I shared the document with two other document management apps and it displays fine in both. One of the two apps supports editing formatted notes and I was able to edit the document, remove the image, shared it back to DEVONthink To Go and now the document works as expected (only 8.8 KB in size).