You can see all the contents when you open some PDFs, but the printed ones are reduced by half, and other documents are printed normally. In this case, you can look at the PDF document itself first.

For the time being, treat every page in the pdf as a picture. It can be displayed as the actual size (i.e. 100%) to see if the length and width are only half of A4 paper, as shown in the following figure:

In this case, Method 1: When printing, check "Reduce document as required" in the printer properties, and then enlarge the size to 200%; This will fill a piece of A4 paper. Similarly, if you encounter other proportional sizes, you can set the size to be enlarged or reduced; If you originally typed a PDF on A4 paper, you only printed half of the document, which may be that the actual size of the document itself is 200% of A4 paper; At this time, when you set "Reduce Document on Demand" in the printer properties, you should check Reduce the size to 50%; As the legend goes:

When the enlargement or reduction is not 100%, for example, 200%; Pay attention to check the page scale in Print and Advanced as "Use original page size", otherwise the printed content may not be centered and the border will have many white edges.

Method 2: If the document is scanned by a third-party scanning software and then saved as a pdf, you can choose to directly save each page of the scanned document as a picture, then import the picture with word, set the margin to 0, print directly after overwriting word, or convert it into a PDF (at this time, convert it into a normal A4 paper size) for printing. Different printer settings may be different, refer to ideas.

There are many other standard questions on the Internet, so you can search for them yourself.