Not 64-bit. Not Windows 10. Not the online bootstrapper that will reach out into the void for files that no longer exist. You need the offline one. You need the 32-bit version. You need Windows 7.
You search for it with surgical precision: "net framework 3.5 offline installer windows 7 32 bit." net framework 3.5 offline installer windows 7 32 bit
And then you wait.
Windows 7, 32-bit, reached End of Life on January 14, 2020. In the eyes of Microsoft, it is a corpse. The automatic update servers are either shut down or deliberately obtuse. The online installer for .NET 3.5 tries to phone home, finds the line dead, and returns a cryptic: "0x800F0906 - CBS_E_TRUST_FAILURE." Not 64-bit
So you turn to the offline installer. The relic. You need the offline one
When you finally see the green progress bar complete— "Installation complete" —something strange happens. The machine does not cheer. There is no confetti. The old ERP software launches. A legacy DLL binds. A printer configured on LPT1 (emulated over USB) spits out a report.