Well NPSH should be measured in M or feet, not pressure.

Either way for this issue you either need a vacuum pump connected to the inlet line or a self priming pump. I'm not sure a self prime will lift 5m though.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

We use some Scot self-primers that will lift up above 25ft, but you gave no indication as to what the discharge performance needs to be. I think they only go up to 7.5HP, which does something like 225gpm/80ft when lifting 15ft.

Typically the pump needs a manual prime if it doesn't have some kind of assist mechanism, the case is opened and filled and that starts the prime to give it something other than air to work with. Depending on the lift required this doesn't always work, or sometimes needs more than one shot. After the initial prime the case should remain flooded, and a foot valve (check valve designed to be the point of suction in cases like this) will keep the suction line flooded to start fully primed from then on, unless the prime is lost.

High capacity auto air vents can be used, alone or in combination with manual air vents. The pump will pass air to the discharge side where it's easier to deal with, but venting is definitely needed to help get things started.

Many solutions to priming a pump, it depends on application.
Once a day then operation non stop all day.
Every 10 minutes.
Fully automatic for unattended operation.
Flow rate.
Product being pumped.
Electric or engine driven pump.
More detail for your application will ensure better answers

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

Google "pumps with built in priming pump" and pick what suits you; also check required vs NPSHa after subtracting frictional losses.

A foot valve with strainer will solve your question, However the mechanical seal operation in this case where there are high chances of air getting into system is critical.
Consult with seal vendor.

A well phrased question has answers in itself!!!

But at some point you need to first fill the inlet line. Foot valves are not always reliable and then you need a second form of filling the inlet line.

However the point about the inlet operating well below atmospheric pressure is a good one - the seals could easily leak air into the liquid unless specifically suitable.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.