upgrade from DYNAMICS C5 to Microsoft Dynamics NAV 2016.

Hi Rehan Satti
It depends on the Dynamics C5 version (Dynamics C5 is a ERP product mainly for Denmark and Island).
If the version is Dynamics C5 2014 or newer it is in fact a NAV (C5 2014=NAV 2013R2 and C5 2015/2016 = NAV 2015/2016. C5 2016 is the last version - it is scheduled to be replaced by Dynamics 365 later this year in Denmark). So on that version you just complete a regular NAV upgrade process.

If it is Dynamics C5 version 2012 or earlier, it is a completely different platform so you are kind of out of luck. This C5 version is based on the discontinued Damgaard XAL / Microsoft XAL platform and has a end-of-life around January 2019.
Beware that the logic in Dynamics C5 2012 and earlier is completely different from Dynamics NAV, so one cannot just transfer all transaction data and expect it to work in NAV. The systems are too different for that.

If it is Dynamics C5 2012 or earlier there exists two approaches:
1. Migrate base data without transactions from C5 to NAV (you could probably use Rapid Start in NAV - C5 can export all data to CSV-files) and do a manuel setup of posting etc. in NAV. The customer will loose history (but can off cause keep history in C5).

2. Get in touch with one of the Danish partners who can do a partly data migration with more or less transaction data to NAV and help you understand C5 customizations etc. The company I work for (www.systemconnect.dk) have around 7.000 existing Dynamics C5 customers, so we are doing this ALL THE TIME :-). We would be happy to help other partners complete this task, but it is NOT a standard process and needs tweaking each time (also because the Dynamics C5 probably have customizations too).
Off cause you can also write the needed code yourself, but the investment will probably not pay off unless you have multiple Dynamics C5 customers you need to migrate to NAV.

You can reach me at gsl@systemconnect.dk if you would like our help.