Note: Time Capsule is shared through AirPort Extreme Wi-Fi router.
For this, you need to run AirPort Extreme utility under Mac OS System Preferences.
To set up a connection, follow the steps below:
turn on Time Capsule;
make sure it is connected to the same Wi-Fi as your iOS device;
launch PDF Expert 6 and check the Nearby section on your iPad or Available devices in the Services tab on iPhone;
if you do not see your device in the Nearby section, please open settings > network > choose "Add account" > choose SMB protocol, establish connection using your credentials. Once done, you should be able to set up SMB connection using your Time Capsule IP address and account name in PDF Expert 6.
Note: Don't forget to mention the Shared folder in the appropriate field.