That’s how it works:
Open the your Dropbox with Tex Touch
Navigate to the folder in your Dropbox you want to work in. Tap on “Set Tex Folder”. You choice will be saved.
You can check your current tex folder in the settings.
Every file you want to compile will be uploaded into this folder.
You can change the folder at any time.
Open your document.
When you want to compile your document proceed with the following steps:
Click the “...” more button in the top right corner.
Tap on “TeX”. Wait until the process is completed (you will see). Tap “PDF” to see you PDF