Where can i download a comprehensive photoshop tutorial pdf file?

The most comprehensive pdf you can get on Photoshop is the Photoshop user guide (hit F1 and look for the link to view/download the pdf guide)... it tells you a lot about every tool, setting, and feature within Photoshop.

If you're looking for an actual tutorial then you need to be more specific about the type of task you want to learn. There are far too many things you can do with Photoshop to be written in a single tutorial. And even if you did find one, it STILL wouldn't be able to cover everything because everyone uses different techniques to do the same kinds of tasks. For example, to remove a subject from an image/background -- Some people prefer using the lasso tool, some prefer the pen tool, some prefer manipulating/using channel information, some use color range (aka chroma keying), some prefer masking.... some use a combination of two or more tools and/or techniques. But no matter which technique they use, they can all be use to do the same exact thing... remove the subject from it's background. To complicate matters even further, these same techniques can also used for other tasks/needs as well.

Don't expect a step-by-step guide to learning PS, nor expect to learn all there is to know about it. There are some things that you will NEVER EVER need, and even if you do, you can just learn it when needed. Otherwise you'll be far too overwhelmed with information. Just learn as you go. If you want to learn how to create a shape, look up tutorials on creating custom shapes. You'll pick up things as you go and eventually you'll be able to figure out on your own how to apply them in completely different situations.