I don’t know if this should be a troubleshooting request, a request for features or a bug.
I am trying to use Devonthink to organize documents some of which are Excel sheets.
I soon learned to link to Excel sheets with the link command.
I had an rtf note where I wanted to make notes of the names of Excel sheets I had been searching for high and low. I copied the name of the sheet and pasted it into an RTF note and was very pleased to see that not only was the name there but I coiuld open the sheet by double clicking on the icon in the RTF note. Imagine my surprise when I opened that RTF note today and find only the text I typed into it - the icon and the name of the Excel sheet are gone. Zilch!
I’m guessing that you had automatic Wiki linking turned on at the time you typed the Excel sheet’s name into the RTF file. If you clicked that link, you would be viewing the link document you had previously created.
The second time you looked at the RTF file, either you had turned off automatic Wiki linking in the preferences, or you didn’t click on the sheet’s name (was it underlined and dark blue, or not?).
Here’s a suggestion for another way of linking to unrecognized file types, which I prefer because I can write notes about the file if I wish:
 Create an RTF document in DT or DT Pro.
 From the Finder, drag one or more Excel sheets onto that RTF document. Links (icon + filename) will be copied into your RTF document at the cursor position. Clicking on such links will open the sheet in Excel. As noted, this would be a convenient way for you to make a list of your Excel sheets, adding descriptions for each if you wish.
As I stated earlier, your suggestions works.
There is just one problem. The Excel Sheet is saved in a different location so I cannot make changes to it if I want it to be saved in the original location.
Can I save an Excel sheet I drag into an RTF note in its original location?