Create Unique Sequence Number in Cell for invoice

Hello. I am new in excel and to this forum.
I have this situation:

I have an invoice template and in one cell I must fill in a unique number and always must increase by 1 . For example if previous number was 300 next number must be 301 etc....
For me this cell is K5.
In more details I want to open the template and automatically K5 cell gets this number from the previous invoice.Also I need to save each invoice automatically and get the name of the file from two different cells with an underscore ( _ ) between in a folder which I will specify. And for the end when I save the file I want to clear a range of cells from the invoice and get ready for the next one.
Can anyone help me please?

Thank you
John

Keep in mind that I have post this thread to other forums as well and if it is answer I will close the thread.The reason for this was that I am in dead end.
http://www.ozgrid.com/forum/showthread.php?t=197548
http://www.mrexcel.com/forum/excel-q...mber-cell.html

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Hi ioannisg,

Check this;http://www.excelforum.com/excel-prog...locations.html

can you post the code?

Originally Posted by Blokeman

can you post the code?

Sure:

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Try the uploaded file;