When someone sends you a PDF, it doesn't mean it's ready to print. PDF is a universal file format that most people can easily read, but there can be several problems with PDF files.
This is not a suitable file for printing. This means that it is prepared in RGB and at the minimum image resolution (at least with the default settings, which I assume that you, as a programmer, have not set Word to CMYK, 300 dpi images...). It can also be prepared from InDesign, but the settings are incorrect. I wrote more about proofreading in my blog
The key to a properly prepared file for submission or printing is a few important things:
1. True color space (CMYK or specific spot Pantone colors)
2. A sufficiently large image in the file (if the image did armenia telegram lead not have enough pixels or dpi before preparing the pdf, it is probably impossible for it to be better afterwards). The minimum is 180 or 200 dpi for printing a 133 line raster and for a 150 line raster at least 210 dpi, the optimal is 300 dpi.
I emphasize: if the image is downloaded from the Internet and is 10Kb, then it will not be any better, even if you increase the number of pixels / dpi in Photoshop. It will just be more "fuzzy", unsharp.
3. Crop marks are not "crosses and problems". They are very important information for the printer. Before printing, several pages are assembled into a single printing plate. Therefore, we need to know the correct size of the final page.
4. Bleed allowances mean that already in the design process, images will be prepared that "look over the edge" of the page. Place them at least 3 mm beyond the edge. Why do we need this? First of all, it is important to know that all machines have some tolerance and a very small line (say 0.2 mm) of white paper next to the black edge is very clearly visible. That is why we print over the edge a few millimeters beyond the edge of the cut. So a 1 mm cutting error will be invisible, but without a bleed it is very visible (if the color is up to the edge).
If you are submitting material for the web, the settings are a little different:
1. RGB
2. number of pixels (web banners), 96 dpi (or otherwise recommended by the advertiser)
3. no crosses or cuts
4. there are no allowances for cropping (but there are allowances for, say, the edge of the screen - a space where text should not be placed because the image is not displayed on certain monitor formats)