C# - Finding The Index Of Characters In A String?

I have a text file that is automatically generated by an older computer system daily. Unfortunately, the columns in this file are not delimited and they are not exactly fixed width (each day the width of each column could change depending on the amount of chars of the data in each column). The file does have column headings, so I want to find the width of each column using the column headings. Here is an example of the column heading row:

JOB_NO[variable amount of white space chars]FILE_NAME[variable amount of ws chars]PROJECT_CODE[variable amount of ws chars][carriage return]

What I want to do is get the index of of the first char in a column and the index of the last white space of a column (from the column heading). I would want to get the index of the "J" in JOB_NUM and the last white space before the "F" in FILE_NAME for the first column.I guess I should also mention that the columns may not always be in the same order from day to day but they will have the same header names. I know I can use the string.indexOf("JOB_NO") to get the index of the start of the column, but how do I get the index of the last white space in each column? (or last whitespace before the next first non-whitespace that denotes the start of the next column)