How to resolve Document Library PDF previews taking up more disk space than the original files

Issue

While examining our document library in a file system, we saw that the storage being used for preview files are taking up three times the amount of disk space as the storage for the original files uploaded to documents and media, leading to disk space usage issues. In particular, PDF files seem to be the largest contributor, with their previews much larger than their original files.

This behavior is expected, as .png files (used for previews) use a lossless compression algorithm, while PDFs can contain images using a lossy compression algorithm. As such, a .png file of the same image can take up more space depending on how many colors are included within the image.
Document previews can be adjusted to fit one's use case using the following portal properties (defaults for 7.2 provided below):
```
    dl.file.entry.preview.enabled=true
...
    dl.file.entry.preview.document.depth=8
    dl.file.entry.preview.document.dpi=300
    dl.file.entry.preview.document.max.height=0
    dl.file.entry.preview.document.max.width=1000
    dl.file.entry.preview.video.height=360
    dl.file.entry.preview.video.width=640
```
- Setting dl.file.entry.preview.enabled=false will disable previews entirely
- Lowering the *.height and *.width will make the previews smaller (saving disk space)
- Lowering *.dpi will decrease the image resolution while retaining the original size

For more information on Image Previews and compatible File Preview Apps, see these articles:
A feature request has also been created to implement a property or other configuration that would exclude certain document file types from having previews generated (to allow more granular preview generation configuration), and can be followed at LPS-115329.