is it possible to get app code from apk and customize it? is it possible to get android socurce code from apk.

i had seen on some tutorial that shows the way to get code from apk just guessting if we can do it really .

please guide they way to do it if possible

i was able to get source code but issue is that when i try to run it in eclipse i see lots of error .
There are decompilers out there, but it's very likely that what you get out of it will be a garbled mess. If the developer used Android's ProGuard, you may not be able to reverse engineer the resulting code. The only site I know of for decompiling is this one.  Be careful and keep it legal.  Source code is intellectual property.  If the developer has a website or says their code is open source, contact them to find their github repo.