Thiel also forced entrepreneurs to ask what they think is true that others don't. With PDF apps, the answer was that there is a gap in between where they can provide a better experience. As you noted, it may not be enough to take on Adobe but it fulfills a niche from which the vision could become broader. See Dropbox who wanted to replace thumb drives and rewritable CD-Rs to popularizing the cloud storage consumer option with all its additional possibilites.