(I didn't download anything.. but it is simple identification merely looking at the posted image.)
That is a mesh object. Either a gradient mesh or an envelope mesh. There's nothing "wrong" with the shape. Meshes merely aren't "simple" objects and don't behave like simple objects. "Anchors" in mesh objects not only serve as ...
For the standard Pen Tool — After pulling a curve, hold down the Alt key and click the last anchor. This breaks the anchor's symmetry. You can then click to create a straight segment, or click-drag to create an un-smooth curve. This is the same functionality as Illustrator only you must hold the Alt key for the click.
For the Freeform Pen Tool — After ...
An alternate workflow option:
create a polygon
select it by clicking inside the polygon with the white arrow tool
adjust the corner widgets (View> Show Corner Widget) to your liking by click/ dragging them in or out
You can always re-adjust the corner radius by re-selecting the shape and changing the corner widget position or you can numerically set ...
The Index Finger has a clipping mask on it to support a gradient fill (which can't be seen because its behind the card).
It's a simple thing to remove.
Choose Object > Clipping Mask > Release from the menu
Select the (now visible) rectangle fill edge and delete it
Select the "hollow" shape for the index finger and fill it with the ...
ADD: The simplest workaround in Illustrator is at the end of this answer. Jump directly to it if you do not like elementary geometry nor methods which are either non-exact or need extra software.
There's an infinite number of possible curves which are tangential with 2 given circles, Actually there exists an infinite number of possible circle arcs ...
Further to some exchange in the comments, the real reason for the problem was discovered.
The reason Expand was greyed out for you is because you used the Brush Tool to make the paths, which applied a brush to the path. It wasn't a basic stroke. This means you when you tried to do Expand the Blend, only Expand Appearance was available, and this expanded the ...
You are getting it almost right, but need to stick to the options under the Blend menu:
Make your blend and select it.
To turn the blend into separate strokes go to Object → Blend → Expand.
This will actually create a group of strokes, which you can then ungroup and edit each piece individually, if needed.
I'm not an Illustrator user, but Inkscape and other programs offer the same feature. According to Adobe's help system, it's called Image Trace in the Illustrator program:
Choose Object > Image Trace > Make to trace with default parameters.
Illustrator converts the image to black and white tracing result by
Results will vary based on the ...