Many older networking textbooks, university lab manuals, and pre-recorded video courses (circa 2012-2015) were built specifically for Packet Tracer 5.x or 6.x. Some lab files ( .pkt ) created in version 6.0.1 may become corrupted or behave unexpectedly when opened in v8.x due to deprecated commands or protocol changes (e.g., differences in OSPF or EIGRP implementation).
Given the risks of malware, we advise the following sources (always scan with Windows Defender or VirusTotal): Many older networking textbooks, university lab manuals, and