Hi
"Is it true that VideoPad checks only clip/picture file name to take it into project - it does'nt "remember" file size & content? "
The project file (.vpj) saves the basic data regarding the clip. Its location and name, the in/out points, sequence position, transitions and effects, subtitles/text/overlay clips, whether muted or not and data regarding any soundtrack associated with the clip and any bookmarks.
The cache file contains a reduced size version of all the clips, images and thumbnails that you see on the editing screen. These are built up as you edit the project or load more clips. The project file (vpj) though contains sufficient data to rebuild the cache file if you happen to delete it. This takes time though and can cause a delay before you can continue to edit your project. If the cache file is still there, obviously the project will load quicker as the images don't need to be created.
"Situation that I have not tested too is.. ..if I have destroyed some file in project (by accident for example) and then try to load project into VideoPad - what happend - project content minus destroyed file will be loaded into VP or even none... 
?"
If you try to load a project (vpj file) for which you have deleted or moved a clip, VP will load the project with the files it has and will , in V 2.41..print the missing file name in Red in the media list and leave a blank frame on the timeline. You can then locate the missing file by clicking its name in the list and browsing to the folder where it has been moved to. If the clip has been deleated then you will need to reload it back to your PC into its original location. If you then reload the project it will be included as normal.
In VP 3.xxx the missing files will be listed and you will be prompted to either delete them or resolve the problem in a similar way to above.
"...For example I can even change clip/picture content in existing project by change its name same as original in project + then replace old clip/picture with same named new clip/picture having total different content?"
Provided the "new" clip has the same name and is in the same location as the "removed" clip, it will appear in the project in place of the "old" clip irrespective of the content. However the in/out positions (your cut edits), subtitles, sound properties, transition effects etc. that applied to the old clip will now be applied to the new clip.
This is the idea behind possibly editing with identically named reduced size clips (or use MPEG2 clips) to increase rendering speeds or reduce synch problems and then changing the folder name when finished to point to the original MPEG4 clips which are then used to produce the final render.
Nat
