This document may have been updated since your installation. You can find the latest version at http://docs.kde.org/development/en/extragear-utils/.
Why is it called "KDiff3"?
Tools named "KDiff" and "KDiff2" (now called "Kompare") already exist. Also "KDiff3" should suggest that it can merge like the "diff3"-tool in the Diff-Tool collection.
Why did I release it under GPL?
I'm using GPL programs for a very long time now and learned very much by having a look at many of the sources. Hence this is my "Thank You" to all programmers that also did so or will do the same.
Some buttons and functions are missing. What's wrong?
You compiled from source but you probably didn't specify the correct KDE-prefix with configure. By default configure wants to install in /usr/local but then KDE can't find the user-interface ressource file (i.e. kdiff3ui.rc). The README-file contains more information about the correct prefix.
Often lines that are similar but not identical appear next to each other but sometimes not. Why?
Lines where only the amount of white space characters is different are treated as "equal" at first, while just one different non-white character causes the lines to be "different". If similar lines appear next to each other, this actually is coincidence but this fortunately is often the case. See also Manual Diff Help.
Why must all conflicts be solved before the merge result can be saved?
For each equal or different section the editor in the merge result window remembers where it begins or ends. This is needed so that conflicts can be solved manually by simply selecting the source button (A, B or C). This information is lost while saving as text and it is too much effort to create a special file format that supports saving and restoring all necessary information.
How can I synchronise the diff and merge views, so that all views show the same text position?
Click into the summary column left of the text. (See also here.)
Why does the editor in the merge result window not have an "undo"-function?
This was too much effort until now. You can always restore a version from one source (A, B or C) by clicking the respective button. For big editing the use of another editor is recommended anyway.
When I removed some text, then suddenly "<No src line>" appeared and cannot be deleted. What does that mean and how can one remove this?
For each equal or different section the editor in the merge result window remembers where it begins or ends. "<No src line>" means that there is nothing left in a section, not even a new line character. This can happen either while merging automatically or by editing. This is no problem, since this hint won't appear in the saved file. If you want the orignal source back just select the section (click on the left summary column) and then click the source button with the needed contents (A/B or C).
Why doesn't KDiff3 support syntax-highlighting?
KDiff3 already uses many colors for difference highlighting. More highlighting would be confusing. Use another editor for this.
Can I use KDiff3 to compare OpenOffice.Org, Word, Excel, PDF-, etc. files?
Although KDiff3 will analyse any kind of file the result will probably not be very satisfactory for you.
KDiff3 was made to compare pure text files. OpenOffice, Word, Excel etc. store much more information in the files (about fonts, pictures, pages, colors etc.) which KDiff3 doesn't know about. So KDiff3 will show you the contents of the file interpreted as pure text, but this might be unreadable or at least it will look very odd.
Since most programs nowadays store their contents in XML-format, you might be able to read it as pure text. So if the change was only small, KDiff3 still might help you.
The best solution if you only want to compare the text (without embedded objects like pictures) is to use "Select All" and "Copy" in your program to copy the interesting text to the clipoard and then in KDiff3 paste the text into either diff input window. (See also Select, Copy And Paste.)
Where has the the directory option "List only deltas" gone?
There are now several "Show"-options in the directory menu. Disabling "Show identical files" will achieve what enabling "List only deltas" used to do.
How can I make a big selection in the diff input window because scrolling takes so long?
Start the selection as usual (click and hold the left mouse button). Then use the navigation keys (e.g. page up, page down) while holding the left mouse button down. (See also Select, Copy And Paste.)
There is so much information here, but your question is still not answered?
Please send me your question. I appreciate every comment.