You can read most documents without downloading them, and every file keeps its earlier revisions, so replacing a drawing never loses the one it replaced.
Previewing a file
Click a file's name, or choose View from its ⋮ menu. PDFs, images, and video open in the preview without downloading.
A PDF you have opened once reopens faster afterwards.
Why versions matter here
Whether your uploading a new schedule or revised drawings, versioning allows you to minimize the number of line items in your folders. Keeping revisions as versions of one file (rather than as Rev A, Rev B and Rev C sitting side by side) means there is never any doubt about which one is current.
Replacing a file with a newer revision
Open the file's ⋮ menu.
Choose Upload new version.
Select the new file.
The file keeps its name, its folder, and any links you have shared. The Version column ticks up, and the previous revision moves into the file's history.
Looking at earlier versions
Choose Version history from the ⋮ menu. From there you can see the earlier revisions, preview them, download one, and restore an older version as the current one.
Every saved version counts toward the project's storage, which is why a project with heavily revised drawings uses more than the current file sizes suggest.