An easy method to reduce the size of a PDF file is to recreate it, removing unnecessary objects, tags and reducing the size of the images. Any software that has a print to PDF function can be used to achieve this. PDF files can also be reduced by using the save as feature which rewrites the entire file and reduces the size unlike the save feature in which the files saved is of larger size, although it is faster. This can be done by using PDF editing tool. Using the same, links, bookmarks, annotations and form fields can also reduce the size. Reducing the image sizes can also be useful to reduce the size of a PDF file noticeably. The images have to be compressed one at a time for more granular control.
Most of the PDF file creators use named destinations which are markers used to spot certain locations in the file or to link another PDF file to a particular spot in the first PDF file. Using 10 (approximately) named destinations can add 1KB to the file size. Hence, it should be used only if it is necessary so that it helps to reduce the size of a PDF file.
One can use PDF optimizer to find out the elements that use more space and can make necessary changes to reduce the size of a PDF file. In optimizing, graphics may be a problem. Graphics can be scaled to occupy lesser space. The dimensions of a bitmap should be as small as possible in a PDF file. But compressing the graphic beforehand can cause noticeable changes in the image. If the PDF is for web or for printing purposes, RGB color space can be used as it occupies lesser space than CMYK. Avoid embedding fonts and use less fonts in the PDF file to minimize the size. Subset fonts which have only the glyphs actually used can minimize the font size bloat and helps to reduce the size of a PDF file.