Link panel is blank

You won't see linked documents if they were not inserted as links, using the FIle>Place or drag and drop for the desktop or finder.

You often see graphics copied and pasted into a document from photoshop, where the area is selected and the operator copies it, and pastes it directly into InDesign.

This won't provide a link to the image.

To get the link back - you could, in theory, choose Embed image, and then unembed the image, you will be prompted whether you want to link to the original or not - do not link to the original - save it to a new location and the image should now be linked.

Hi,

Please always include in your query the version of InDesign and the operating system you are using.

Also, consider including screenshots to help us understand better your question and send you the correct answer quicker.

You can use an application like https://www.screentogif.com/ to insert animated screenshots.

Remember that some issues can be fixed by restoring preferences (scroll down to Restore) https://helpx.adobe.com/ie/indesign/using/setting-preferences.html

The links panel should display the images, MS Word/Excel, pdf and other resources (even another InDesign) you have added in your document using  File > Place for example. Embedded files will not be listed in your Links panel.

More at Manage linked or embedded graphics in Adobe InDesign

What OS (exact version)?

What InDesign (exact version)?

What do you mean by Document? Text file, image file?

Why do you believe it should appear in Links panel?

How do you bring it into InDesign layout? Using File>Place, or maybe just copy/pasting?

Assuming it's a text file, and you're using (correct) File>Place routine, did you check settings in Preferences > File Handling tab > Links area?

Sorry for so many questions, it's a summer time, our mentalists have their leave, and you managed to say us almost nothing…