You probably don't need to know this at this late date, but I would use a foreach loop container.
First, create a variable to hold the name of the file for subsequent steps in the package. Create and edit the foreach loop container and put your filename wildcard specification (*.txt, or ??????.csv, or INCOMING*.*, or whatever your requirements) for the collection. Have it assign the filename to the variable you have created, and all other tasks within the container can then use that variable to determine which file is being worked on.
The next iteration of the foreach loop will assign the next filename, and will stop execution where there are no more files selected. Note that you cannot specify the order in which these files are picked up; my experience is that they are retrieved in a date/time modified order, but there are techniques where you can create a sorted list of files which a web search should reveal to you readily.
Hope this helps.