Thanks everyone for help and I do believe that all you guys want to give a true technical explanation regarding my issue.
Above there are two image size screen shots regarding the picture I'm talking about.
You guys say that I'm doing wrong this and that and I believe that, so could you please based on Photoshop image size window tell me what to change to increase the pixel number and have a standard A4 picture?
I read that to have a decent print the picture has to have at least 240 ppi so my intent is to increase the number of pixels.
I think that in my case resampling won't affect too much quality unless we want to zoom 800+ in the picture to find problems.
The original picture is "nearly" standard A4 so it's a bit smaller and this will create a problem because I need to stretch it to fit in the final A4 print.
I've attached the sample from the original picture.
Again, I printed a master sample and in my opinion it looks good but I still need your advices before committing any big mistake.
I digitally stretched the picture in a way that the final print has a white border all around (decided by the printer) but nothing is cut out from the picture.
[ATTACH]47956[/ATTACH]
Could Photoshop Elements be more suitable for my job? What if I export to pdf format then I can automatically print duplex or booklet? Can Elements from more than one picture or a folder create a pdf document? Will the document change picture's properties and quality?
I chatted with an Adobe representative and of course has was just clueless, he pretended to explain me printer's settings while diverting the main issue, finally he said that Elements cannot do it!
Thanks to everyone.