A link in InDesign is a reference to an external file. A common type of link is a picture. Your InDesign document contains a low-resolution preview of the picture, and when you go to print your document or make a PDF out of it, InDesign follows the link to get the high-resolution original.
To check links, go to the links palette. If no symbol appears at the right side of any link, then you have no problems. If a symbol is there, then you might have a problem. There are three common symbols that could appear.
The embedded symbol. Your link is embedded inside your InDesign Document. There is nothing to worry about.
The modified symbol. The date of the preview in InDesign of your link does not match the date of the link. Click the Update Link button
to update your link.
The broken symbol. Your link is broken. This means that InDesign cannot find your file. Click the Relink button
to tell InDesign where it is.
You can highlight all of your links to relink them all. This is especially helpful when something basic happens like you moved or renamed your links folder. To fix all of your links at once, highlight them all by clicking on the first one and shift-clicking on the last, and click the Relink button
. InDesign will ask you for the location of the first one, and it will see that the others are all there, too, and it will follow suite automatically.
If you click on a link on the Links palette, you can go to where it is used on your page by clicking the "Go To Link" button
.