Do reference managers require that the user inputs the info for each PDF that they have and assign an ID to it, or is some (or all) of that process done automatically? I know I should've started using a reference manager long ago and hope that I don't have to go through all of the articles on my computer!
Using a reference manager can save a lot of time and reduce errors - I highly recommend it. Yes, most reference managers will automatically extract the relevant information from a PDF, but it is always worth looking it over as it won't be correct 100% of the time.
For example, I am familiar with Mendeley, which is free to download and has desktop apps for Mac, Windows, and Linux. Mendeley will automatically populate fields such as title, author names, journal name, volume, page numbers, keywords, url, and DOI, directly from a PDF. These fields can be edited, removed, or added to as needed.
I think it is also worth mentioning that Mendeley has an extension for Google Chrome and Firefox browsers called Mendeley Web Importer, which allows the user to easily add full text PDFs with the associated metadata (and does not require a previously downloaded copy of the PDF stored on a computer). This feature has also saved me a lot of time.