This is a Vigenere cipher. The keyword is FIVE letters long.
PEFDN FIUQC UCRJD PLXTK FLJFJ TYHWC UGJXQ BAJXR ICXTL FQFXY WCLJL FLJYM QLTHC FXDTS TBTZJ EBFAC UUPJL FPJWW GCKYF MYYYC SIKYF FWNUF FLYJV UCYTJ ESTZR IUYYF FEJDU BMKNT FFJYR FLXQM OADTS XIZQB IUAJR IYSIM OYFKP FKZJL DSHTS ONNSM SXJWR PYXYY CFNXF IIBRS DBJAC SSKND UBQJR UYWMY EVJJL DUJXY SMMND UYIDM VQTZJ EBFAC UBJSS OMMND UYIYF FFJYR FLXFL ELJHM OMYWS DNJIR IYRJQ TULJR IYPJW CSYMC XUDBY TVZKD Z
Please don't spoil the puzzle by posting a solution. Post help, or requests for help, by all means - but be circumspect.
A solution will appear in one week - so I won't be providing help :)