A Shih Tzu is a proud and regal dog that likes things very clean and doesn't really get trained. You can show a Shih Tzu what you expect it to do, but in the end if it does not adopt the behavior then you have a long road ahead of you. Punishment and negative reinforcement will cause all of your training to be undone and you may even have to reconnect with your Shih Tzu after any punishment. Your Shih Tzu only understands positive reinforcement so be patient and use good training.
Punishment never works with a Shih Tzu so don't try, it will only undo any training you have done. You need to always be engaging in rewards and praise for good activity and ignoring bad activity.
Housebreaking a Shih Tzu is a long process that can take months and the one thing you do not want to do is keep introducing new things into the process. This will confuse your dog and set back your training by months.
Even under the most ideal conditions, with the best-behaved Shih Tzu ever, housebreaking can still take upwards of six months so patience is a virtue. Shih Tzu paper training could make housebreaking even more difficult so be certain that you have given all standard housebreaking methods a chance before resorting to the paper.
Since setting up a confined living area for your Shih Tzu is a standard first step in the housebreaking process it is assumed that the Shih Tzu is probably soiling in areas just outside the living area. If this is the case you can try expanding their living area to include the soiled area and move their bedding close to, but not on, the soiled spot. Shih Tzu dogs do not soil where they sleep so perhaps after moving it's bedding near a soiled spot it may start to think that outside is a better option.
If you want to try Shih Tzu paper training then you will need to begin moving its living area around to be near the main soiled area. Cover the area in layers of paper and make sure the living space is near, but not on, the soiled area. Slowly begin to move the living area, and the papers, towards the door to the outside. Always clean the papers regularly, keep a small amount of soiled paper with fresh paper so the dog knows it is an area to use, and praise the dog for using the paper.
Housebreaking a Shih Tzu can be one of the most frustrating things you have ever tried but you need to be patient and stick with a housebreaking routine.
Breaking that routine by moving the living space and adding newspapers will probably set your housebreaking back to square one so be patient and stick with the standard methods before you try the papers.