[How to change file format?]

Since no one will help me on my other thread, Can some please,please just tell me how to change the file format, .pdn format and i need it to be an .png format. This picture I created was made out of 4 sepreat pictures all of them were screen shots taken from the game I play. Three of them came out as a .png but 1 some how came out as an .pnd so can some please help me.

[I need an uploader for .pdn formated file.]

I dont post here very much as you can tell so i dont really know hwere it would have gone.

And i think might have said it wrong, I need to but this .pdn image on another forum that i goto. So that link from before did not really help.

[I need an uploader for .pdn formated file.]

like the title say, I use Imageshack.us and i'm trying to upload a .pdn formated file. So if u could either tell me how to change it or give me a link to a uploader that can do it, i'll be very thank full.

[Help]

I'm trying to add a sig that i made on another forums and i donty know how to make it into a url code. they use phpBB BBCode with an [img/] thing. it says to but the img url between them but how do u get the url code?