Tools - Options - Debugging - Symbols.

Select checkbox "Microsoft Symbol Servers".

Visual Studio downloads PDBs automatically.

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/008c8fb3-b704-4f2c-bd85-adcee56c574f/Untitled.png

Source:

VS 2017 [RESOLVED] Cannot find or open the PDB file-VBForums