This is quite a common request - and the answer is
YES (but not the way you want it to)
…which is why I have this FAQ page.
Under the hood, the Apple Pencil looks to apps like a finger. So all apps work with the Apple Pencil. The Apple Pencil is a little more advanced than that (but not much!) It also does the following:
Tells an app how much pressure is being applied
Tells an app what angle you are holding it relative to the screen
Tells an app more accurately (and frequently) where the pencil is on screen.
What it doesn’t do is ‘out the box’:
Provide any kind of ‘ink’ technology (e.g. drawing smooth lines that change based on how you hold it or press it.)
Provide any shape detection technology (you can’t draw shapes with it and have them turned into real geometric shapes)
Provide any handwriting recognition (you can’t have handwriting turned into real text.)
Provide and highlighting capability (you can’t scribble over a document and highlight text.)
Now obviously all the above is possible - since it’s done in the Notes app and some other 3rd party apps. The kicker here is that those features are all implemented within the apps themselves. There is nothing in iOS that helps here. This means that each app must implement its own drawing/highlighting/handwriting technology.
iThoughts has the Doodle feature which enables people to draw simple diagrams with their finger (or Pencil.) It works better with the Pencil due to the accuracy - but the Pencil is not a requirement.
Handwriting to text conversion is not possible in iThoughts. This would require me to license 3rd party technology (or develop my own) and this is not financially viable.
[UPDATE] iOS13 has now comes with a simple ‘drawing system’ that takes advantage of the Pencil. This can be embedded in 3rd party apps. iThoughts uses this to enable you to ‘markup’ existing images and PDF files. There is also an option (in the System Settings for iThoughts) to use this drawing system in place of the previous Doodle feature. This will enable you to create nice looking ‘bitmap’ images using the pencil (similar to those you can create using the Notes app.) The downside is that they are bitmaps (whereas the previous Doodle system was vector based.) Bitmaps don’t scale very well and they take up more disk space.
Still there is no handwriting recognition or shape recognition - but this can’t be too far off given the work that Apple is putting into AI…