Hi @delfino2107 ,
You need to clean the scanner glass window beneath the ADF. A speck of dirt or grime etc on the glass window will cause a vertical line to appear on the output document.
''Be careful when cleaning''. See the Cautions advisory notes in the image below. A slightly damp microfibre cloth seems to work quite well.
Here’s an image taken from p.34 of the [http://h10032.www1.hp.com/ctg/Manual/c04204791|user manual] that shows the two separate scanner windows. The smaller one on the left is used for the ADF and the larger one is for flatbed scanning.
[image|2194219]
(click on image to enlarge for better viewing)