Protec Soprano Sax Pro Pac Instrument Case

Q: How large is the pocket? Is it large enough to hold a regular sized (A4) music sheet?

No it is not more like put 2 iphones side by side wide at the most

Q: Can this case accommodate a non detachable neck sopranos saxophone?

This case does NOT accommodate a one-piece soprano. The top of the horn will end up resting on the accessory box, and my 1925 Buescher was resting on the octave key mechanism and rod, which would bend if there was any kind of impact. I followed the advice of another commenter and removed it myself because I love everything else about the case and didn’t want to return it and get something else. It’s difficult to do though and you can easily rip the lining. Once it was removed though, it rested nicely on the movable supports that come with the case. I ended up putting a towel where the accessory box was just to take up the extra space and prevent any movement if it takes a really big shock.