[WB19,20,21] fseek for external file

I need to traverse an external file, back and forth from beginning to end several times because the strings aren't in any order. I tried using fseek to return to the beginning of the file by passing it 0, fpbeginning and also -16981, fpcurrent (which is fsize of the file). But neither of these work. Will I have to close and reopen the file several times in order to get back to the beginning?

Thanks in advance for any help on this...