When uploading images (jpg, png), the thumbnail becomes a preview of the image. Why doesn't this happen with a pdf document? There are several people who have made similar requests. I found 3 with a total of 122 likes. Maybe more? In any case not few and does seem like a justified request that deserves attention. Maybe for other file formats as well? For a tool like ClickUp, this is definitely a must and currently a deficiency.