Four and a half years ago, I started playing baroque pipe organ music. Many sheet music is available online in PDF format, one of the main sources being the International Music Score Library Project (imslp.org).
Having the PDFs available is great, though not sufficient to practice and play the pieces. Further modificatons are required, and the Preview app of macOS provides almost all editing features needed. To cope with a couple of issues, I’ve developed several workarounds.
I use preview to combine multiple PDFs into one and to add several annotations to the sheet music. This includes text like tempo and registrations. The main purpose, however, is fingering, which mainly consists of numbers above respectively below the staves. I also use straight and bezier lines to mark the beginning and end of fragments, or to mark notes of a stave to be played with the other hand.
Avoid editing annotations
Editing annotations, like text boxes or lines, often leads to unexpected behaviour. Text suddenly appears bigger as formatted. Text boxes suddenly switch from transparent to black backgound colour (as visible in the depictions). Annotation lines become partly or completely invisible. To avoid those effects, avoid editing annotations completely, and be careful when copying PDF pages from one document to another. Instead, delete them and create a new one. This saves a lot of hassle and makes Preview more joyful to use.
Making annotations permanent
Appearently it is vendor specific how annotations are saved with the PDF. As a consequence, the annotations aren’t visible when displaying the PDF on other devices, e.g. an Android tablet. Fortunately, from Preview’s print dialog, it is very easy to export the PDF to PostScript (PS). Then I open the resulting file in Preview again and re-export it from the print dialog as PDF. This way, the annotations become true PDF elements which are visible on the tablet. As a drawback, the annotations are no longer editable, so make sure to still keep and make edits via the original PDF.
BTW: This step also helped me with an online print service which was unable to get the original PDF through the raster image processor.
Saving PS on macOS 10.15 (Catalina)
For unknown reasons, Preview’s Postscript export only works once on Catalina after each reboot. Any further attempt results in an error message. Some people had luck by configuring additional printer drivers for this task. In case this is not what you’d like to do, you can open your PDF in the Safari browser and print it to Postscript there. I have no clue whether Apple intends to get this ironed out in the near future. Since other issues haven’t been addressed for quite some time, I presume I have to get used to the workaround.
macOS makes Sheet Music Editing easy right out of the box. I do not need any additional tools thanks to Preview. The abovementioned simple workarounds are useful to circumvent some hiccups.