C# software for merging files

I need a software for merging files. The files are text files form log unit. The format is timestamp in ms, message ID, message contents. There is one entry at each line. There are two (or more files) from two (or more) devices. These two files need to be merged into one. There are two problems: 1.) The timestamp has some offset and this offset changes in time 2.) The files are big (100k+lines/messages) There is a solution for first problem. Each second there is a synchronization message in all files. Example: File 1: 1 SYNC MSG 0 2 MSG A 30 MSG B File 2: 101 SYNC MSG 0 111 MSG C 112 MSG D Output: 1 SYNC MSG 0 2 MSG A 11 MSG C (111-101+1) 12 MSG D (111-101+2) 30 MSG B The offset is not constant all the time but vary. The problem 2 means you can not simply load all files into array. The solution must be in C# (MS Visual prefered) and no GUI is necessary. I can provide you example files.