Yes, Photoshop is backwards compatible, however, once you save the file in CS5 you will not be able to use it in CS4 anymore.
You can use files saved in CS5 in almost any other version and any page layout program which supports psd files, here i mean to save as psd. When saving turn on Maximize PSD and PSB File Compatibility in Edit > Preferences > File Handling.
Find the Adobe Photoshop CS4.exe file and double click on it. To make this process faster, before you click ir, right click on the EXE file and choose create shortcut. Right click on the shortcut and click cut. Go to your desktop and click paste. Then all you have to do is double click on the shortcut and it will automatically open.
Nowhere, Photoshop is not free software.
Photoshop CS4 Bible Check Here http://www.amazon.com/Photoshop-CS4-Bible-Stacy-Cates/dp/0470345179
Filter -> Blur
You can go to www.adobe.com/downloads and get a trial version of Adobe Photoshop CS4 for free.
CS4 Extended is the legal version that you must buy. CS4 Portable is a free, illegal version that does all the same things as CS4 Extended, the only difference is that you can't add plug-ins
CS4 is version of software, and the name before CS4 is stand name of Software, for example Photoshop CS4 is: software Photoshop and version CS4. The Name of Software is Photoshop not Photo shop, please don't change. ---------------- If you want to know more about it then open photo shop and click on the help menu and select About Photoshop sub menu and then you will see and Photoshop about window. You can read there more about it.
cs5 is better
they are listed in filters menu
The average price of Adobe Photoshop CS4 is $1299. The software package is available from several online retailers for this same price with varying shipping costs offered.
The extended versions have all of the features the normal ones do but they offer extra features such as the ability to import and edit 3D graphics, video enhancement and more tools to use for editing images etc.
you probably mean plug-ins?As you install any software,if you mean actions then copy and paste in C:\Program Files\Adobe\Adobe Photoshop CS4\Presets\Actions