Standard PDFs are not print-ready. They may have poor quality images and colors, which may not print as intended or print at a very low quality. Most modern software packages can create a high-resolution print-ready PDF.

PDF checklist:

• Check the bleed around all edges and check for crop marks.

• Check that images don't look overly pixelated onscreen, resolution of 300 dpi or higher is best.

• This one’s so important! proof read it before sending to print.

Select the File Format

Quality beats speed when it comes to choosing the best file format for your print ready PDF. Rather than picking the fastest file format, you’ll want the file formats that have the highest quality. Know that file formats all compress information differently. Select 'High Quality Print' or similar to achieve quality.

Pick High Resolution

One of the most important steps you can take to prepare your PDF is to ensure that your images are crystal clear. You want high resolution, which is a function of how much data is in the digital image. For print, images should be at least 300 PPI (pixels per inch).

Add Crop Marks

Crop marks are two perpendicular tick marks at each corner of a printed piece, and they instruct the printer where the final trim size ends. Professional printers print on oversized paper with bleeds, these tick marks show the printer exactly where to make the cuts.

Add Bleed (3mm)

Printers use bleed to create a seamless look, with the image or background printing right to (and through) the edge of the paper. This is difficult to achieve by printing on the exact size paper, as you may have noticed with smaller office printers, the printer will leave a border untouched since it cannot print right up to the edge. 
So to achieve a continuous background, professionals print the image beyond the final desired size and then cut back to that desired size.