"I've bought the uVision 1 from a compagny which wasn't using it anymore. So they've sold it to me for a low price."

Maybe now you know why!? ;-)

"There was only the software and no documentation."

How can you RTFM if there is no manual? ;-)

"That's why I'm working with the uVision 2 PDF files."

That's probably more of a hindrance than a help - uVision-2 is significantly different from uVision-1.

"But as it's for own applications I couldn't afford to buy the uVision 2."

Have you looked at the free "Evaluation" version?
(be sure to read the limitations carefully)

Raisonance has a slightly-less-limited free "Evaluation" version, and there was a recent post from someone else offering a free 8051 'C' compiler.
Also, take a look at the 'Links' page for other tool options.

I really think you're making life unnecessarily difficult for yourself using an out-of-date, undocumented, unsupported tool like uVision-1 - especially as a beginner!