how can I watch a film which I have downloaded onto my iPad pro on a television, using a lead, without access to wifi?

What model of iPad Pro do you have exactly?

For First and second 12.9" iPad Pros and 9.7" and 10.5" iPad Pros: Lightning Digital AV Adapter - Lightning to HDMI - Apple

For 3rd and 4th generation 12.9" iPad Pros, and 11" iPad Pros: USB-C Digital AV Multiport Adapter - Apple

and a good quality HDMI cable.

The Samsung UE32M5500 has 3 HDMI ports, so I'd go with a USB-C to HDMI adapter. Apple sells these two adapters compatible with your device:

• USB-C Digital AV Multiport Adapter ($69)
• Belkin USB-C to HDMI Adapter ($50)

Of these two I'd recommend the more expensive first one, since you can charge the iPad through the adapter while it's plugged in, and it also has that extra USB-A port, might come in useful later. You could look at cheaper USB-C to HDMI 3rd party adapters on online stores, but only buy a well-reviewed one that's confirmed to work with iPad Pros.

You'll also need an HDMI cable if you don't have one. Any cheap HDMI cable will work for the TV's 1920x1080 (1080p) signal, there won't be distortion or anything, because it's a digital signal as opposed to analog. At 4K resolution the cable type would matter, as some cables support a newer version of HDMI, which is needed for 4K 60 Hz playback instead of just 4K 30 Hz, but at your TV's 1080p maximum resolution any HDMI cable will work the same.

Thanks for confirming the exact model of the iPad Pro and that your iPadOS software version is 13.5.1, I've written all this with that in mind.

It would help a lot if you could post the model of the TV and the iPad, to find out what kind of a connection can be used (e.g. AirPlay, or Lightning to HDMI adapter). Since it's an iPad Pro and running iOS 10, I'm assuming it's a Lightning port model and not a USB-C one, is that right?