How to remove plastic film on window pane

A quick Wikipedia search leads me to say its Polyolefin (also see Shrink Wrap):

The most commonly used shrink wrap is polyolefin. It is available in a variety of thicknesses, clarities, strengths and shrink ratios. The two primary films can be either crosslinked, or non crosslinked. Other shrink films include PVC and several other compositions.

Source: http://en.wikipedia.org/wiki/Shrink_wrap

Any adhesive that will adhere to "plastics" should work fine.

Soundproofing as it relates to windows is all about mass -- the denser the materials, the more sound reduction you'll get. PVC is, indeed, typically more dense than the far more lightweight aluminium and so will will resist noise transfer more. However, the amount of surface area made up by the frame is absolutely dwarfed by the glass itself. Any differences in the frame will be massively overshadowed by the properties of the glass, make it a moot point.

PVC/Vinyl windows do a far better job of restricting conductive heat as they are a much better insulator than aluminium. Aluminium is really one of the worst materials to use from an insulation standpoint.

However, PVC/Vinyl will eventually "melt" in a hot environment. Recycled PVC will do so far faster than virgin PVC, but even the latter will eventually sag enough that opening and closing the window will be tricky. Assume maybe 15-20 years.

Aluminium will last indefinitely. That and the price are typically the two big selling points of that material.

In short, neither has a true advantage from a soundproofing perspective (the glass does quite a bit, though) but PVC is a better choice from an insulation standpoint if you are willing to replace the window every 15 years or so. If you don't care about the insulation value and don't want to replace the window, then aluminium is the way to go.