So I’m getting a new IPhone and I have a app with lots of downloaded content it’s called ‘Documents’. I don’t want to have to redownload all the content so I’m wondering if I transfer my SIM card to my new phone from my old one will everything still be there?
The sim card has no relation to your iPhone's data, or transferring content. All the sim card has is your number and carrier settings.
Transferring the sim card from one phone to another has no effect on your apps data or files.
If you are letting Documents store your files in iCloud, then they should come back when you log in to iCloud on the new iPhone.
Otherwise restoring a backup taken from the old phone onto the new iPhone, should transfer all the files inside the apps that are not being synced to iCloud. See here: Transfer content from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
The sim card has no relation to your iPhone's data, or transferring content. All the sim card has is your number and carrier settings.
Transferring the sim card from one phone to another has no effect on your apps data or files.
If you are letting Documents store your files in iCloud, then they should come back when you log in to iCloud on the new iPhone.
Otherwise restoring a backup taken from the old phone onto the new iPhone, should transfer all the files inside the apps that are not being synced to iCloud. See here: Transfer content from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
Nothing is stored on the SIM card by the iPhone.
You will have to backup your old device and restore to the new one.
Transfer of SIM card
