Dear Gregory Wallace,
Thank you for posting your request on History Hub!
Since the link you referenced is from the Federal Bureau of Investigation, we suggest that you contact them about the contents. Their web site is https://www.fbi.gov/services/information-management/foipa#Obtaining-FBI%20Records.
We hope this is helpful. Best of luck with your research!
Gregory Wallace, the link/URL you provided points to the official web site of the US Federal Bureau of Investigation. I followed the link and it contains, in PDF form, official FBI documents released pursuant to the Freedom of Information Act.
I don't know what "JFK,Jr/Biden plot" you are referring to but the released documents do refer to a 1994 letter sent to Sen. Joseph Biden by an unknown subject or "unsub" describing Biden as a "traitor", stating "you must die", and bearing the signature of one John F. Kennedy Jr. The FBI documents indicate that four latent fingerprints were recovered from the envelope and/or letter but they could not be matched because there was "no suspect" for fingerprint comparisons.
In sum, the link is legitimate and it links to actual FBI documents. However, the letter addressed to Biden seemingly was either falsely attributed to John F. Kennedy, Jr. (i.e. the signature was forged by an impostor) or it was authored by someone of the same name who was not the son of the late President Kennedy.