Google-drive – If I replace a PDF file in Google Drive, will the share link stay the same, or will I have to give out a new one

If you want to be able to use the same share link you need to upload your new file as a new revision not a new file. Every time you upload a new file it will generate a new share link. However, if you upload a revision it will keep the same share link every time.

To upload a new version of a file using the web interface:

1. Log into your drive and find the file or folder you wish to revise.
2. Tick the checkbox next to the file or folder.
3. From the dropdown that comes from the More button, click on Manage Revisions.
   a. If you are viewing a file it will be under the File menu.
4. A dialog box will appear in the top part of the box click the link "Upload a new revision"

Old revisions are kept per Google for 30 days or 100 revisions whichever comes first. Ofcourse from this same option you can delete or save revisions yourself.

Samples:

For the moment, you have to build the URL manually.

https://docs.google.com/uc?export=download&id=YourIndividualID

Where YourIndividualID is the ID of the respective document (zip file). You get it either from the URL or by clicking File → Share and copying it from the sharing URL.

Source.