How to open a bitmap file and draw a string on it with C++?

If you're going to do it with the Windows API (really it's GDI component), You need to know about handling memory DC's. That's quit a long topic give you a full answer.
 
Here're some sources :
>> Programming Windows Charles Petzold (see chap. 14) -http://www.amazon.com/Programming-Windows%C2%AE-Edition-Microsoft-Series/dp/157231995X/ref=sr_1_1?ie=UTF8&qid=1358346269&sr=8-1&keywords=programming+windows
>> A Codeproject Article - http://www.codeproject.com/Articles/224754/Guide-to-Win32-Memory-DC
>> Search google - There's plenty of things about DCs

hi dear sergey
if you work with visual c++, below code helps you:
 

CImage i;
i.Load(_T("a.bmp"));
CDC cdc;
cdc.Attach(i.GetDC());
cdc.TextOut(_T("Hello world"),10,10);
cdc.Detach();
i.ReleaseDC();