Definitions
.pdf = Adobe file format. The format is more of a picture, so it's really lousy for downloading data. Avoid at all costs.
.csv files = commas separated values file. Values, such as numbers or texts are separated in a table by commas...sometimes you can see them and sometimes you can't until the file has been converted to text.
.prn files and .txt files= these are text type files, that are as basic as you can get. They can be useful to Excel users though because if the values in .txt or .prn files are separated by commas, tabs or any other single character, they can be imported successfully into Excel.
.xls files = .xls files are the files native to Microsoft Excel. Occasionally data will come to you in this fashion, but generally you wind up having to convert it to .xls to work with it. Frequently, students have to save it then to .dbf format to use it easily in a GIS.
.dbf files = .dbf format is database format. Many of the older database programs (which are different than spreadsheet programs like Excel) use .dbf. Most GIS programs, since they are database driven, require data be in .dbf format first. .dbf generally have DBF2, or DBF3 or DBF4 options. I try to use 3 or 4. The most important thing to remember is that column headings in a .dbf are really separate from the data and MAY NOT CONTAIN SPACES. This is very different than .xls format, where spaces are OK and the first row of data also frequently functions as the column heading
