A PDF can become large because it contains high-resolution images, scanned pages, embedded fonts, or extra document data. One practical solution is to use a PDF optimization tool that reduces image resolution and removes unnecessary information. To shrink pdf file size, select a suitable compression level based on how you plan to use the document. For online sharing, moderate compression is often enough. For printing, retain higher image quality. Always review the compressed version to ensure that important details, charts, and text are still clear.